Substrate attracting and holding system for use in exposure apparatus

ABSTRACT

A substrate attracting and holding system includes a holding table for holding a substrate, a protrusion provided on the holding table, the protrusion being disposed to be placed in a predetermined positional relationship with a position of an alignment mark to be used for processing the substrate or a position with respect to which an alignment mark is to be produced.

FIELD OF THE INVENTION AND RELATED ART

[0001] This invention relates to a substrate attracting and holdingsystem for grasping a substrate or workpiece and, more particularly, toa substrate attracting and holding system for use in a semiconductormanufacturing apparatus, a liquid crystal substrate manufacturingapparatus, a magnetic head manufacturing apparatus, a semiconductorinspection apparatus, a liquid crystal inspection apparatus, or amagnetic head inspection apparatus or for use in manufacture of amicro-machine, for example. In another aspect, the invention concerns anexposure apparatus or a device manufacturing method using such asubstrate attracting and holding system.

[0002] In reduction projection exposure apparatuses used in themanufacture of semiconductor devices, for example, enlargement of thenumerical aperture (NA) has been promoted to meet miniaturization of adevice (chip). Although the resolution is improved by a larger numericalaperture, the effective depth of focus is shortened on the other hand.Thus, in order to maintain the resolution while keeping a sufficientpractical depth, attempts have been made reduce the curvature of imagefield of a projection optical system or to improve the wafer flatness inregard to wafer thickness non-uniformness or flatness precision of achuck.

[0003] One factor for causing degradation of the flatness of a wafersurface is the presence of a foreign particle caught between a chuck anda wafer. If a foreign particle of a few microns is once caughttherebetween, the wafer at that portion is deformed and raised thereby.Where the effective depth of focus is 1 micron or less, local defocusoccurs there and, in a worst case, a pattern defect is produced. Inorder to avoid degradation of the product yield rate due to such foreignparticles, based on the probability, pin contact chucks (pin chucks)wherein the contact rate between a chuck and a wafer is reduced to aminimum are used prevalently.

[0004] As regards a machine for processing a substrate such as asemiconductor wafer, for semiconductor device manufacture, or a liquidcrystal substrate, for liquid crystal display device manufacture, forexample, a projection exposure apparatus, generally it uses a substrateattracting and holding system based on a vacuum attraction force to holdand secure a substrate (workpiece) and to correct any warp thereof tokeep its flatness. FIG. 31 shows an example of such substrate attractingand holding system. In the substrate attracting and holding system(chuck) 201 illustrated, a substrate carrying plane is defined by acarrying table which comprises a plurality of pin contact typeprotrusions 202 disposed in a grid and a peripheral rim type protrusion203 provided at the peripheral portion of the carrying plane forsupporting the peripheral portion of a substrate. Also, there aresuction holes 205 formed at the carrying plane where the contact typeprotrusions are provided, which holes are communicated with a vacuumpiping system for reducing the pressure between the carrying plane and asubstrate to be carried thereon.

[0005] The substrate attracting and holding system of a structure suchas described above is used in a semiconductor exposure apparatus, forexample. A wafer which is a substrate is conveyed onto the chuck 201 bymeans of a conveying system. After the wafer is placed on the chuck 201,it is held fixed on the chuck 201 by vacuum attraction applied throughthe attraction holes 205. Here, in order to reduce the probability ofoccurrence of deformation of the wafer surface due to catching a foreignparticle between the chuck carrying table and the wafer, the total areaof the substrate supporting protrusions distributed along the carryingplane is made small.

[0006] In the substrate attracting and holding system such as describedabove, the layout of the substrate supporting protrusions which providethe chuck carrying table is determined without any specific concern tothe processing region on the substrate. It is set without any positionalrelationship with the substrate processing region. Namely, if thesubstrate processing region changes, the same chuck is usedcontinuously. Therefore, if the surface of a substrate is deformed as aresult of the attraction and holding of the substrate, the deformationmay cause not only a deformation of that portion of the substrate in avertical direction but also a distortion along the plane of thesubstrate. Further, the layout of the substrate supporting protrusionsof the chuck is determined without any specific concern to the layout ofalignment marks of a substrate. If the alignment mark layout of thesubstrate changes, the same chuck is used continuously. While adeformation of the substrate surface resulting from the attraction andholding of the substrate may cause an error in the coordinate of analignment mark, since the relationship between each substrate alignmentmarks and each substrate supporting protrusions of the chuck is unknown,it is not possible to correct the coordinate error and, therefore, theregistration precision is degraded.

[0007] On the other hand, in a lithographic process among semiconductormanufacturing processes in which a very fine pattern is transferred byexposure, in consideration of the depth of focus being decreased withminiaturization of the device or a coordinate error of a pattern to betransferred, the flatness of a substrate as held by a chuck has to bedecreased as much as possible. If the substrate has a distortion along ahorizontal direction caused by the deformation of the substrate surface,the error in the coordinate of an alignment mark of the substratebecomes large as a result of it. Additionally, if such coordinate erroris different in each region (hereinafter, “shot”) to be processed by asingle operation or in each semiconductor device (hereinafter, “die”),since a semiconductor device is produced by superposing variouspatterns, the pattern registration is much degraded. If there is a largedifference between shots, it can not be corrected easily and, in a worstcase, a defect of a semiconductor device is produced.

[0008] It is known that, in a pin chuck, a wafer is deformed and warpedbetween pins of the chuck due to vacuum attraction and that this causesdegradation of the flatness of the wafer surface. Many proposals havebeen made to solve this problem. For example, Japanese Patent No.2574818 proposes a structure wherein a ring-like groove is formed in anouter peripheral portion of a chuck and wherein pins are provided in acentral portion, inside the groove, at a pin pitch of 2 mm or less, soas to keep good wafer flatness at the chuck peripheral portion and goodwafer flatness within the pin pitch at the chuck central portion. Inthis patent, it is stated that, with a pin chuck having pins disposed ina grid, the flatness within the pin pitch can be approximated by a modelof a beam having both ends free-supported and that, from a desiredflatness, a required pin pitch can be made 2 mm or less. However, theapproximation with the beam having both ends free-supported means thatthe pin pitch as a whole is determined by using the condition for thesupport with the free end at the outer peripheral portion whichcondition is worse than that at the central portion. There is nodisclosure about determining optimum pin pitches for the flatness at theouter peripheral portion and at the central portion, respectively.Therefore, this causes an inconvenience that the pin pitch at thecentral portion becomes smaller than as required and, as a result, thecontact rate becomes larger than as required.

[0009] In an attempt to solving this problem, Japanese Patent No.2821678 proposes a structure wherein the pin pitch at a central portionof a chuck is made larger than that at an outer peripheral portion ofthe chuck, thereby to improve the wafer flatness at the chuck outerperipheral portion and the chuck central portion while keeping thecontact rate small. According to this proposal, it is suggested that theflatness within the pin pitch at the peripheral portion can beapproximated with a model of a beam having one end fixed and another endfree-supported, while the flatness within the pin pitch at the centralportion can be approximated with a model of a beam having both endsfixed, and that the ratio between the pin pitches at the peripheralportion and the central portion can be optimized.

[0010] In the proposal made in Japanese Patent No. 2821678, however,there is an assumption that the attraction force is even at the outerperipheral portion of the chuck and at the central portion of it. Thereis no disclosure about determining optimum attraction forces for thewafer flatness at the chuck outer peripheral portion and the chuckcentral portion, respectively. Also, there is no disclosure aboutdetermining an optimum relationship between the pin pitch and theattraction force, for the wafer flatness.

[0011] Although such wafer flatness, that is, degradation of the wafersurface flatness due to a warp produced within the pin pitch, is in facta problem to be solved, there is a much more serious problem that adistortion (wafer distortion) is in practice produced due to the warpwithin the pin pitch. For example, where a wafer of a 200 mm diameterbeing currently widely used is placed on and attracted to a pin chuckhaving pins arrayed in a grid with a pin pitch 2 mm, there may occur awafer distortion of about {fraction (1/2.6)} of the wafer flatness. In asemiconductor process of 0.25 micron rule, being mass-producedcurrently, the tolerance for the wafer flatness is 80 nm if it is set tobe 10% of a depth of focus 800 nm, whereas the tolerance for the waferdistortion is 5 nm if it is set to be 10% of an overlay precision 50 nm.This value when converted into a wafer flatness becomes equal to 13 nmwhich is much smaller than 80 nm. Namely, it is seen that, as comparedwith the flatness as required by the depth of focus, the flatness asrequired by the overlay precision is much more strict. Conventionally,the flatness correction has been made so as to reduce the wafer flatnessto a tolerance, whereas it has never been done so as to reduce the waferdistortion to a tolerance. As a result, the wafer distortion may be morethan the tolerance, causing a degraded overlay precision and a decreasedyield rate. Alternatively, an additional process margin may be needed,which may obstruct further miniaturization of a semiconductor device orfurther enlargement of integration of it.

[0012] In the aforementioned Japanese Patent No. 2821678, it is statedthat, when the flatness at the outer peripheral portion of a wafer ismade better, a positional deviation of an alignment mark at the waferperipheral portion can be reduced like a positional deviation of analignment mark at the wafer central portion. However, there is noquantitative statement about the alignment mark positional deviation.Further, there is no recognition of the inconvenience of a waferdistortion resulting from a warp within the pin pitch at the chuckcentral portion. There is no disclosure about determining an optimumrelationship between the pin pitch and the attraction force, in respectto the wafer distortion. There is no disclosure about determining therelationship with respect to each of the peripheral portion and thecentral portion, respectively. Namely, there is no disclosure ofreducing the wafer distortion to a tolerance.

SUMMARY OF THE INVENTION

[0013] It is accordingly an object of the present invention to provide asubstrate attracting and holding method, a substrate attracting andholding system, an exposure apparatus and/or a device manufacturingmethod using a substrate attracting and holding system, by which theinfluence, upon a substrate processing precision, of an error incoordinate of an alignment mark to be produced by deformation of thesurface of the substrate resulting from the attraction and holding ofthe substrate.

[0014] In accordance with an aspect of the present invention, there isprovided a substrate attracting and holding system, comprising: aholding table for holding a substrate; a protrusion provided on saidholding table, said protrusion being disposed to be placed in apredetermined positional relationship with a position of an alignmentmark to be used for processing the substrate or a position with respectto which an alignment mark is to be produced.

[0015] It is another object of the present invention to provide asubstrate attracting and holding system, an exposure apparatus and/or adevice manufacturing method using a substrate attracting and holdingsystem, by which a distortion or degradation of a flatness of thesurface of a substrate such as a wafer, for example, due to adeformation of the substrate surface to be produced when the substrateis attracted and held by using a plurality of protrusions, can bereduced so that the substrate can be attracted and held in an optimumstate and that an overlay precision can be improved.

[0016] In accordance with another aspect of the present invention, thereis provided a substrate attracting and holding system having a pluralityof protrusions for supporting a substrate, for attracting and holdingthe substrate supported on the protrusions, characterized in that adisposition pitch L of the protrusions and an attraction force P of thesubstrate are set so as to satisfy a relation:

P·L ³≦[36·E·h ² ·dxdy]/[{square root}{square root over (3)}·k·c]

[0017] where dxdy is a distortion tolerance, E is a longitudinalelasticity coefficient, h is a thickness of the substrate, c is acorrection coefficient based on the protrusion disposition and k is aneutral plane correction coefficient.

[0018] These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIGS. 1A-1C are schematic views best showing features of asubstrate attracting and holding method according to the presentinvention, wherein FIG. 1A is a plan view of an embodiment of asubstrate attracting and holding system arranged in accordance with thesubstrate attracting and holding method of the present invention, FIG.1B is a plan view of a substrate and it shows an example of dispositionof shots or dies on a substrate, and FIG. 1C shows an example ofpatterns of alignment marks.

[0020]FIG. 2 is a schematic and sectional view of a substrate attractingand holding system in a state in which a substrate is being attractedand held thereby.

[0021]FIG. 3 is a schematic view for explaining an example of errors incoordinate, per a shot, to be produced as a result of attraction andholding of a substrate.

[0022]FIG. 4 is a plan view of another embodiment of a substrateattracting and holding system according to the present invention.

[0023]FIG. 5 is a schematic and sectional view of a substrate attractingand holding system according to a further embodiment of the presentinvention, in a state in which a substrate is being attracted and heldthereby.

[0024] FIGS. 6A-6C are schematic views of a yet further embodiment ofthe present invention, wherein FIG. 6A is a plan view of a substrateattracting and holding system of this embodiment, FIG. 6B is a plan viewof a substrate as attracted and held by the substrate attracting andholding system of this embodiment, and FIG. 6C is a view for explainingthe relationship between substrate supporting protrusions of thesubstrate attracting and holding system of this embodiment and theposition where alignment marks are produced.

[0025] FIGS. 7A-7C are schematic views of a still further embodiment ofthe present invention, wherein FIG. 7A is a plan view of a substrateattracting and holding system of this embodiment, FIG. 7B is a view forexplaining the relationship between substrate supporting protrusions ofthe substrate attracting and holding system of this embodiment and theposition where alignment marks are produced, and FIG. 7C is afragmentary perspective view of a portion adjacent to the position wherealignment marks are provided, in a state wherein a substrate is beingattracted and held by the substrate attracting and holding system ofthis embodiment.

[0026]FIG. 8 is a schematic view of the structure of an exposureapparatus.

[0027] FIGS. 9A-9C are schematic views, respectively, wherein FIG. 9Ashows a warp of a substrate as attracted and held by protrusions, FIG.9B shows a model of a beam having both ends secured, bearing a uniformlydistributed load, and FIG. 9C is a view for explaining the relationbetween the substrate surface and a neutral plane not deformed by a warpof the substrate.

[0028]FIG. 10 is a schematic view of the structure of a mechanism forreplacement of substrates and chucks.

[0029]FIGS. 11A and 11B show another embodiment of a substrateattracting and holding system according to the present invention,wherein FIG. 11A is a plan view and FIG. 11B is a sectional view of thesame.

[0030]FIG. 12 is a plan view of a substrate attracting and holdingsystem according to a further embodiment of the present invention.

[0031]FIG. 13 is a sectional view for explaining the state of asubstrate and a central portion of a chuck as the substrate is attractedand held by a substrate attracting and holding system according to thepresent invention.

[0032]FIG. 14 is a schematic view of a model of a beam having both endsfixed, bearing a uniformly distributed load corresponding to the stageof a warp of a substrate at a central portion of a chuck.

[0033]FIG. 15 is a schematic view for explaining bending moments andflexure curves curves in the double-ends fixed beam of FIG. 14.

[0034]FIG. 16 is a schematic view for explaining distortion of asubstrate.

[0035]FIG. 17 is a schematic view for explaining disposition of pins ina grid layout.

[0036]FIG. 18 is a schematic view for explaining disposition of pins ina 60-deg. staggering grid layout.

[0037]FIG. 19 is a schematic and sectional view for explaining the stateof a substrate and an outer peripheral portion of a chuck, when thesubstrate is attracted and held by a substrate attracting and holdingsystem according to the present invention.

[0038]FIG. 20 is a schematic view of a beam having an end fixed andanother free end, bearing a uniformly distributed load corresponding tothe state of a warp of a substrate, at the outer peripheral portion ofthe chuck.

[0039]FIG. 21 is a schematic and sectional view of an outer peripheralportion of a chuck of a substrate attracting and holding system,according to a yet further embodiment of the present invention.

[0040]FIG. 22 is a schematic and sectional view for explaining anotherexample of a chuck central portion.

[0041]FIG. 23 is a schematic and sectional view for explaining anotherexample of a chuck outer peripheral portion.

[0042]FIG. 24 is a schematic and sectional view for explaining anotherexample of pin-like protrusions in a substrate attracting and holdingsystem of the present invention.

[0043]FIG. 25 is a graph for explaining an example of a vacuum pressureat the central portion of a substrate and the range of pin pitch, in asubstrate attracting and holding system of the present invention.

[0044]FIG. 26 is a graph for explaining an example of a vacuum pressureat the outer peripheral portion of a substrate and the range of pinpitch, in a substrate attracting and holding system of the presentinvention.

[0045]FIGS. 27A and 27B are graphs, respectively, wherein FIG. 27A showsflexure curves of a wafer within the pin pitch, and FIG. 27B shows theshape of a distribution of wafer distortion within the pin pitch.

[0046]FIG. 28 is a schematic view of the structure of an exposureapparatus.

[0047]FIG. 29 is a flow chart of semiconductor device manufacturingprocesses.

[0048]FIG. 30 is a flow chart for explaining details of a wafer processincluded in the procedure of FIG. 29.

[0049]FIG. 31 is a plan view of a substrate attracting and holdingsystem of known type.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] Preferred embodiments of the present invention will now bedescribed with reference to the accompanying drawings.

[0051] [First Embodiment]

[0052] FIGS. 1A-1C best show features of a substrate attracting andholding method according to the present invention, wherein FIG. 1A is aplan view of an embodiment of a substrate attracting and holding systemarranged in accordance with the substrate attracting and holding methodof the present invention, FIG. 1B is a plan view of a substrate and itshows an example of disposition of shots or dies on a substrate, andFIG. 1C shows an example of patterns of alignment marks.

[0053] Denoted in FIG. 1A at 1 is a chuck which comprises a substrateattracting and holding system to be mounted on a chuck stage of asemiconductor exposure apparatus, for example. In FIG. 1B, denoted at100 is a substrate such as a wafer to be attracted and held by the chuck1. Denoted at 101 is a region (shot) of the substrate 100 which regionis to be processed by a single operation. Alternatively, it denotesboundaries (scribe lines) for defining each semiconductor chip (die). Asregards alignment marks of the substrate 100, alignment marks arealready formed at positions as depicted by crosses 10 and triangles 11.Alternatively, alignment marks are going to be produced at thesepositions. At each position of the cross 10, there is an alignment mark12 (FIG. 1C) which is a mark for position measurement with respect to Xdirection. At each position of the triangle 11, there is an alignmentmark 13 which is a mark for position measurement with respect to Ydirection. Here, an alignment mark may be an alignment mark havingalready been provided on a substrate, or it may be an alignment mark tobe produced on the substrate for the subsequent process.

[0054] In the chuck 1 of FIG. 1A, there are protrusions 2 which providea carrying table for carrying a substrate 100 thereon and which supportthe substrate thereon. The protrusions 2 include rim type protrusions 2a each comprising a rim-like protrusion having its top surface finishedwith a high flatness and a vacuum suction groove formed at the center ofthe width of the top thereof. In this embodiment, these protrusion aredisposed along the scribe lines 101 of the shots on the substrate 100,and thus about the scribe lines 101. With the layout of the rim typeprotrusions 2 a as described above, when the substate 100 is attractedand held by the chuck 1, alignment marks of the substrate can beconstantly placed above the protrusions 2 a. Denoted at 3 is a ring-likeprotrusion being provided at an outer peripheral portion of the chuck 1.It comprises a rim-like protrusion and a vacuum suction groove. Denotedat 4 is a region between the ring-like protrusion 3 and the protrusions2 a. In the region 4, substrate supporting protrusions and vacuumsuction groove may be provided, as required. Denoted at 5 are suctionholes which are communicated with a vacuum suction unit 8 (FIG. 2) forholding a substrate by attraction. These holes are formed to becommunicated with suction grooves of the protrusions 2 a and 3,respectively. Denoted at 6 are opening bores for adjusting a gaspressure in a space between the chuck 1 and the substrate 100 asattracted and held by the chuck 1. Each of these bores 6 is formed in azone as divided by the protrusions 2 a, that is, in a portion inside ashot of the substrate 100. As shown in FIG. 2, these bores 6 arecommunicated with a pressure adjusting unit 7. Further, the protrusions2 a and 3 of the carrying table for supporting the substrate 100 maypreferably be arranged so that the total area contacting the substrate100 is 10% or less of the area of the substrate surface.

[0055] With the structure of the chuck 1 described above, the substrate100 when placed on the chuck 1 is attracted by suction through thesuction holes 5 in response to the operation of the vacuum suction unit8, whereby it is attracted to and held on the rim type protrusions 2 aand 3. Then, by controlling the pressure adjusting unit 7, gasdischarging or gas supplying is performed to the space between the chuck1 and the substrate 100 being attracted and held by the chuck 1, wherebythe pressure in that space can be adjusted.

[0056] As described above, when the substrate 100 is held by vacuumattraction while being aligned with the chuck 1 as in this embodiment,the scribe line 101 portion of the substrate is attracted and secured bythe vacuum suction grooves provided at the protrusions 2 a, disposedalong the scribe lines 101 of the shots of the substrate 100. As aresult of it, as shown in FIG. 2, a flexure deformation is caused at thesurface of the substrate 100. Such deformation of the substrate surfacealso causes distortion of the substrate along a horizontal plane.Namely, due to such horizontal distortion, in each shot there ariseerrors in coordinate as a result of deformation of the substratesurface, such as shown in FIG. 3, for example. In FIG. 3, each dotdepicts a position inside a shot on the substrate, and the length ofeach line represents the magnitude of the coordinate error in theposition at that dot. Since these coordinate errors in each shot aredetermined by the amount of inclination of the substrate surface, thecoordinate error is small in a portion where the tilt of the substratesurface is small, near horizontal. In FIG. 2, at the scribe line 101portion as denoted at 21 and at the central portion of a shot as denotedby 22, the coordinate error is small (in FIG. 3, the portioncorresponding to the scribe line 101 portion at 21 is not illustrated).Therefore, if the alignment marks 12 and 13 of the substrate 100 areprovided inside a shot (except the scribe line), then they are largelyinfluenced by the coordinate errors such as shown in FIG. 3. In thisembodiment, however, the alignment marks of the substate are disposedinside the scribe line 101. This portion of the substrate corresponds tothe position shown at 21 in FIG. 2, and it is supported by the rim typeprotrusions 2 a having a vacuum suction groove. As a result, theposition where an alignment marks is present is held substantiallyhorizontal and, therefore, the alignment mark can be kept substantiallywithout being influenced by the coordinate error caused by theattraction and holding of the substrate.

[0057] Even in cases where the procedure for the substrate processingadvances and changing the the alignment mark forming position becomesnecessary, the same advantageous results are attainable by selection ofany position, as long as it is inside the scribe line. Further, in thisembodiment, the central portion of the shot corresponds to the positionshown at 22 in FIG. 2, and it is the position not influenced by thecoordinate error resulting from the deformation of the substrate surfaceby the substrate attraction. Therefore, an alignment mark can be formedthere. Furthermore, by adjusting the gas pressure in the space betweenthe chuck 1 and the substrate 100 through the function of the pressureadjusting unit 7, the region not influenced by the coordinate error asdenoted at 22 in FIG. 2 can be extended. Thus, the region without beinginfluenced by the coordinate error can be extended as required, suchthat the region for placement of alignment marks can be enlarged.

[0058] The alignment mark 12 shown in FIG. 1C is a mark for positiondetection with respect to X direction. The necessary condition for thelocation of the mark to avoid the influence of the coordinate errorresulting from deformation of the substrate surface, is that thesubstrate surface has no inclination at least in X direction. Anyinclination in Y direction does not affect the position detection in theX direction. Similarly, the alignment mark 13 shown in FIG. 1C is a markfor position detection with respect to Y direction. The necessarycondition for the location of the mark to avoid the influence of thecoordinate error resulting from deformation of the substrate surface, isthat the substrate surface has no inclination at least in Y direction.Any inclination in X direction does not affect the position detectionwith respect to Y direction. In consideration of the above, in thisembodiment, a mark for position detection in X direction may preferablybe provided on a scribe line which is substantially parallel to the Xdirection, while a mark for position detection in Y direction maypreferably be provided on a scribe line which is substantially parallelto Y direction.

[0059] As described above, the whole or a portion of the layout ofprotrusions of the carrying table which are distributed on the carryingsurface of the chuck for carrying a substrate, is determined so that aparticular positional relationship or a particular shape is definedthereby with respect to the positions of all the alignment marks of thesubstrate or to the positions where alignment marks are going to beproduced. Thus, if, for example, the positions of all the alignmentmarks of the substrate or the positions where alignment marks are to beproduced are set to be placed above the protrusions of the carryingtable, then the alignment marks are not influenced by the deformation ofthe substrate surface, resulting from the attraction and holding of thesubstrate. Consequently, the coordinate error of the alignment markresulting from the deformation of the substrate surface can be reducedand, thus, degradation of the substrate processing precision or of theregistration precision can be prevented effectively.

[0060] [Second Embodiment]

[0061] Referring now to FIG. 4, another embodiment of a substrateattracting and holding system of the present invention will bedescribed.

[0062] In this embodiment, as regards the protrusions for supporting asubstrate, the rim type protrusions 2 a of the embodiment shown in FIG.1A are replaced by pin contact type protrusions 2 b and, additionally,the alignment mark forming positions 10 and 11 of the substrate 100shown in FIG. 1B are placed at centers of the disposed protrusions 2 b.In FIG. 4, scribe lines 101 of the substrate are depicted by brokenlines, and crosses and triangles at 10 and 11 correspond to thealignment mark forming positions. Placing each alignment mark at thecenter of the disposed pin contact type protrusions 2 b as illustratedis equivalent to providing an alignment mark at a position 22 in thesectional view of FIG. 2 where there is flexure of the substrate. At thecentral portion of the protrusion layout, the coordinate error is smallas the central portion illustrated in FIG. 3.

[0063] Further, in this embodiment, the support for the processingregion of the substrate is all provided by the pin contact typeprotrusions 2 b and, therefore, the contact area between the chuck andthe substrate can be made smaller than that in the preceding embodiment.This is effective to further reduce the influence of a foreign particlecaught between the chuck 1 and a substrate held thereby.

[0064] Further, even when changing the alignment mark forming positionbecomes necessary with the advancement of the procedure of substrateprocessing, the same advantageous results are attainable in thisembodiment by providing another alignment mark at the center of otherprotrusions 2 b. Further, in this embodiment, the location of thesubstrate surface to be placed just above the pin contact typeprotrusions 2 b is at the position corresponding to the position 21 inFIG. 2. It is the position not influenced by the coordinate errorattributable to the deformation of the substrate surface caused by theholding of the substrate. Thus, an alignment mark can be provided there.

[0065] Further, in the embodiment of FIG. 4, there is alignment marksprovided on the chuck 1, for bringing the chuck 1 and the substrate 100into a particular positional relationship. More specifically, in aportion of the chuck 1 not to be covered by a substrate 100 as the sameis attracted and held by the chuck, for example, at zones 9, plural setsof alignment marks such as at 12 and 13 in FIG. 1C may be provided. Likethe preceding embodiment, the substrate 100 may be provided withalignment marks 12 (FIG. 1C) at positions of crosses 10, and alignmentmarks 13 (FIG. 1C) at positions of triangles 11. The positional relationbetween the chuck 1 and the substrate 100 held by the chuck 1 may bemeasured by using an alignment scope 108 (see FIG. 8) and a chuck stage107 (FIG. 8) of an exposure apparatus, and the positional relationbetween them may be adjusted by using a driving mechanism (not shown).Thereafter, the substrate 100 may be held fixed. With this procedure,the alignment mark layout on the substrate and the protrusion layout ofthe chuck can be brought into a particular positional relationship suchas, for example, placing each alignment mark of the substrate at thecenter of the layout of the pin contact type protrusions 2 b of thechuck 1. The alignment marks may be those generally used forregistration of a projected image of a reticle with a substrate. Sinceexposure apparatuses are usually equipped with the function of analignment scope, advantageously there is no necessity of adding aspecial function to the exposure apparatus.

[0066] [Third Embodiment]

[0067]FIG. 5 shows a substrate attracting and holding system accordingto another embodiment of the present invention. This embodiment is anexample wherein the protrusion for supporting a substrate is notprovided with a vacuum suction groove. As regards the protrusion, thisembodiment uses pin contact type protrusions 2 b like those of theembodiment of FIG. 4. Further, the suction holes 5 communicated with avacuum suction unit in the FIG. 4 embodiment are formed as opening bores6 being communicated with a pressure adjusting unit 7. In thisembodiment, with this pressure adjusting unit 7, the gas pressure in thespace between the chuck 1 and the substrate 100 is adjusted at anegative pressure side, relative to the pressure at the top face of thesubstrate, whereby a substrate attracting function is provided also withthis adjustment. Substantially the same advantageous results as of theembodiment of FIG. 2 are attainable with this structure. Further, in theembodiments of FIGS. 2 and 5, the structure may be modified so thatdifferent pressure adjustments are performed to the opening bores 6opposed to the substrate 100. This meets substrates having a warp as awhole or a large local flexure, for example.

[0068] [Fourth Embodiment]

[0069] Referring to FIGS. 6A-6C, a substrate attracting and holdingsystem according to another embodiment of the present invention will bedescribed.

[0070] In the embodiments described above, the alignment mark formingposition is placed inside the shot layout (an array of plural processingregions) such as upon a scribe line of a substrate or at a centralportion of a shot on the substrate. This embodiment concerns an examplewherein alignment marks of a substrate are provided outside the shotlayout and wherein the coordinate error of the alignment mark can bereduced without being influenced by deformation such as a flexure of thesubstrate surface caused by the substrate holding and attraction.

[0071]FIG. 6A is a plan view of a chuck according to this embodiment,and FIG. 6B is a plan view of a substrate to be attracted and held bythe chuck. FIG. 6C shows the relationship between substrate supportingprotrusions of the chuck and alignment mark forming positions on thesubstrate.

[0072] In the substrate 100 to be attracted to and held by the chuck 1of this embodiment, as shown in FIG. 6B, there are X-direction positionmeasuring alignment marks 10 (depicted by crosses) and Y-directionposition measuring alignment marks 11 (depicted by triangles) which areprovided outside the shot layout (an array of plural processing regionsas divided by scribe lines 101).

[0073] The chuck 1 of this embodiment has, as shown in FIG. 6A,substrate supporting protrusions of a carrying table which comprise anumber of pin contact type protrusions 2 b disposed in a grid-like arrayinside the region corresponding to the shot layout of the substrate, aswell as a ring-like rim type protrusion 3 including a rim-likeprotrusion formed at an outer peripheral portion of the chuck 1 and avacuum suction groove. Further, there are a number of pin contact typeprotrusions 2 b(o) which are arrayed in an oblong shape at plurallocations (eight locations in the drawing) inside a region 4 between thering-like protrusion 3 at the outer peripheral portion and the pincontact type protrusions 2 b (i.e., the region outside the shot layoutof the substrate). Additionally, there are suction holes 5 beingcommunicated with a vacuum suction unit for attraction of a substrate,which holes are provided in the vacuum suction groove of the rim typeprotrusion 3 and also in the region 4 between the ring-like protrusion 3at the outer peripheral portion and the protrusions 2 b. The pin contacttype protrusions 2 b(o) arrayed in an oblong shape are disposed tosurround the alignment mark forming positions 10 and 11 on the substrate100, as illustrated. Additionally, these protrusions are placed in suchpositional relationship that the alignment mark forming positions 10 and11 of the substrate is set at a location where there occurs nocoordinate error as a result of deformation of the surface of thesubstrate as the same is attracted, for example, at a positionequivalent to the position 22 shown in FIG. 2, not being influenced bythe coordinate error. Also, the pin contact type protrusions 2 b arrayedin a grid are disposed with a spacing (pitch) corresponding to {fraction(1/10)} of the spacing (pitch) of the shots on the substrate 100.

[0074] With the structure of this embodiment as described above, even ina case where alignment marks of the substrate are formed outside theshot layout, when the substrate 100 is attracted and held by the chuck1, the portion surrounding the alignment mark forming positions 10 and11 of the substrate is supported by the pin contact type protrusions 2b(o) arrayed in an oblong shape. Further, the alignment mark formingpositions 10 and 11 are placed in such positional relationship with thepin contact type protrusions 2 b(o) of oblong shape array that they arelocated at a place where no coordinate error occurs. Therefore, theinfluence of deformation of the substrate surface such as warp caused byattraction and holding of the substrate can be avoided. The coordinateerror of the alignment mark can be reduced, and degradation of thesubstrate processing precision or registration precision can beprevented.

[0075] As long as the alignment mark forming position on the substrateis placed at a location equivalent to the position 22 in FIG. 2relatively to the substrate supporting protrusions as the substrate isattracted and held thereby, the substrate supporting protrusions are notlimited to the pin contact type protrusion and they may be provided by arim type protrusion or protrusions. Further, the shape of the array ofthe substrate supporting protrusions surrounding the alignment markforming position is not limited to an oblong shape. It may have atriangular shape, a polygonal shape or an elliptical shape. Further, asubstrate supporting protrusion may be provided at a portioncorresponding to the alignment mark forming position outside the shotlayout of the substrate, so that the alignment mark forming position ofthe substrate is supported by this supporting protrusion. This enablesthat the alignment mark forming position is supported substantiallyhorizontally, like the position 21 shown in FIG. 2, thereby to removethe coordinate error of the alignment mark. In that occasion, similarly,degradation of the substrate processing precision and registrationprecision can be prevented.

[0076] [Fifth Embodiment]

[0077] Referring to FIGS. 7A-7C, a substrate attracting and holdingsystem according to another embodiment of the present invention will bedescribed.

[0078] This embodiment is a modified form of the embodiment shown inFIGS. 6A-6C. Like the preceding embodiment, when alignment marks of asubstrate are formed outside the shot layout, this embodiment enablesreduction of a coordinate error of the alignment mark without beinginfluenced by deformation of the substrate surface such as flexurecaused by attraction and holding of the substrate.

[0079]FIG. 7A is a plan view of a chuck of this embodiment, and FIG. 7Bshows the relationship between substrate supporting protrusions of thechuck and alignment mark forming positions on a substrate. FIG. 7C is afragmentary perspective view in which a portion around an alignment markforming position of a substrate as the same is attracted and held on thechuck is illustrated in a section.

[0080] The substrate 100 to be attracted and held by the chuck 1 of thisembodiment is similar to that shown in FIG. 6B, and there are alignmentmark forming positions 10 (depicted by crosses) and alignment markforming positions 11 (depicted by triangles) which are disposed outsidethe shot layout. The chuck 1 of this embodiment has, as shown in FIG.7A, substrate supporting protrusions of a carrying table which comprisea number of pin contact type protrusions 2 b disposed in a grid-likearray inside the region corresponding to the shot layout of thesubstrate, as well as a ring-like rim type protrusion 3 including arim-like protrusion formed at an outer peripheral portion of the chuck 1and a vacuum suction groove. Further, there are a number of pin contacttype protrusions 2 c(o) which are arrayed in an oblong shape at plurallocations (eight locations in the drawing) inside a region 4 between thering-like protrusion 3 at the outer peripheral portion and the pincontact type protrusions 2 b (i.e., the region outside the shot layoutof the substrate). Additionally, there are suction holes 5 beingcommunicated with a vacuum suction unit for attraction of a substrate,which holes are provided in the vacuum suction groove of the rim typeprotrusion 3 and also in the region 4 between the ring-like protrusion 3at the outer peripheral portion and the protrusions 2 b. Also, there areopening bores 6 in the zones as defined by the rim-like protrusions 2c(o) disposed in an oblong shape, which bores are communicated with apressure adjusting unit 7 (FIG. 7C). This pressure adjusting unit 7serves to perform gas discharging or gas suction to the space betweenthe chuck 1 and the substrate 100 as the substrate is held by the chuck,to thereby adjust the gas pressure in that space. The pin contact typeprotrusions 2 c(o) arrayed in an oblong shape are disposed to surround aportion corresponding to the alignment mark forming positions 10 and 11on the substrate 100, like the embodiment of FIGS. 6A-6C. Additionally,these protrusions are placed in such positional relationship that thealignment mark forming positions 10 and 11 of the substrate are set at alocation where there occurs no coordinate error as a result ofdeformation of the surface of the substrate as the same is attracted,for example, at a position equivalent to the position 22 shown in FIG.2, not being influenced by the coordinate error.

[0081] With the structure of this embodiment as described above, inaddition to the advantageous effects as attainable with the embodimentof FIGS. 6A-6C, the gas pressure inside the space between the chuck 1and the substrate 100 at the zone as separated by the rim-likeprotrusions 2 c(o) can be adjusted by gas discharging or gas suctionmade to that space by means of the pressure adjusting unit 7. Thisenables adjustment of the amount of flexure of the substrate 100 in thatregion, as the same is supported by the rim-like protrusions 2 c(o) whenthe substrate is attracted and held. Thus, it enables appropriateadjustment of the surface deformation of the substrate 100 at thealignment mark forming positions or of a portion around them, thereby toperform flatness correction of the substrate surface. This extends theregion of the substrate surface not influenced by the deformation suchas flexure, for example, to be caused by attraction and holding of thesubstrate, and thus enlargement of the region where an alignment markcan be formed.

[0082] In accordance with this embodiment, as described, the alignmentmark forming positions 10 and 11 of the substrate are not influenced bydeformation such as flexure of the substrate surface due to theattraction and holding of the substrate, such that the coordinate errorof the alignment mark can be avoided positively. Further, the substratein the zone as divided by the rim-like protrusions 2 c(o) can be heldsubstantially horizontally and, therefore, the range for forming analignment mark can be enlarged. Thus, also with this embodiment,degradation of the substrate processing precision or registrationprecision can be prevented.

[0083] In the embodiments as described above, the position of analignment mark or the position where an alignment mark is to be formedand a protrusion layout adjacent to that position are placed in aparticular positional relationship with each other. More specifically,the positions of alignment marks of the substrate or the positions wherealignment marks are going to be produced are set at such location lessinfluenced by deformation of the substrate surface resulting from theattraction and holding of the substrate. This effectively reduces thecoordinate error of the alignment mark resulting from the deformation ofthe substrate surface.

[0084] As regards the alignment mark position or the alignment markforming position, when the position of an alignment mark of a substrateor the position where an alignment mark is to be produced and the layoutof substrate supporting protrusions adjacent to it is placed in aparticular positional relationship, it is possible to predictdeformation of the substrate surface due to the attraction and holdingof the substrate. Therefore, it is possible to predict and estimate thecoordinate error of the alignment mark to be caused by the deformationof the substrate surface. Thus, when the alignment mark is measured,correction may be made to the measurement result to correct thecoordinate error of the alignment mark due to deformation of thesubstrate, as calculated beforehand. This accomplished further reductionof the adverse influence.

[0085] Even if the alignment mark position or the alignment mark formingposition can not be set exactly at the location as described in thepreceding embodiments, an exposure apparatus such as shown in FIG. 8,for example, may be used to calculate the coordinate error of thealignment mark on the basis of the combination of the disposition of thealignment mark on the substrate or the alignment mark forming positionand the disposition of the protrusions of the chuck. By taking theresult of calculation into account for the result of detection of thealignment mark through an alignment scope, magnification adjustment ordistortion adjustment of a projection optical system may be made. Thisenables optimum superposition of a projected image of a reticle with apattern on the substrate.

[0086] The calculation of the coordinate error may be made by using afunction for calculation of the coordinate error, or alternatively itmay be made by using a table prepared in accordance with the positionalrelation between the alignment mark position or alignment mark formingposition and the protrusions adjacent to it.

[0087] [Sixth Embodiment]

[0088] Referring to FIG. 8, an exposure apparatus will be described.

[0089] Denoted in FIG. 8 at 103 is a reticle or mask (hereinafter,“reticle”) which is an original having formed thereon a pattern to betransferred by exposure to a substrate 100 such as a wafer, for example.The reticle 103 is held by a reticle stage 106. Denoted at 107 is achuck stage which is movable along a horizontal plane (X-Y plane) whilecarrying a chuck 1 thereon. Denoted at 108 is an alignment scope formeasuring the positional relationship between the exposure apparatus andthe substrate or between the substrate and the chuck. Denoted at 111 isa projection optical system having a function for adjustingmagnification or distortion of a projection lens. Denoted at 112 is acontrol unit for calculating or calibrating a coordinate error of analignment mark due to distortion of the substrate surface, with respectto the result of detection of the alignment mark, and for specifying theadjustment of the projection optical system 111.

[0090] Exposure light passing through the reticle 103 is reduced inscale by the projection optical system 111, and it is projected on asubstrate 100 being attracted and held by the chuck 1. The substrate 100is coated beforehand with a small thickness resist material which is aphotosensitive material adapted to effectively cause a chemical reactionin response to irradiation with the exposure light. It functions as anetching mask in a subsequent process.

[0091] With the structure of the exposure apparatus as described above,an error in the coordinate of an alignment mark to be produced bydeformation of the substrate surface attributable to the attraction andholding of the substrate can be calculated once the combination of thealignment mark forming position inside the substrate and the dispositionof the protrusions of the chuck is determined. Therefore, even if thealignment mark position can not be set exactly at the location asdescribed with reference to the preceding embodiments, the coordinateerror of the alignment mark can be calculated by the control unit 12 onthe basis of the combination of the alignment mark disposition on thesubstrate and the disposition of the substrate supporting protrusions ofthe chuck. By taking the result of calculation into account in respectto the result of detection of the alignment mark through the alignmentscope 108, the magnification or distortion of the projection opticalsystem 111 can be adjusted to assure optimum superposition of aprojected image of the reticle 103 with the pattern of the substrate100.

[0092] A tolerance of alignment for an alignment mark of a substratewith the disposition of protrusions of a chuck for supporting thesubstrate can be estimated by approximation using a model such asfollows. FIG. 9A shows flexure of a substrate as attracted to and heldby protrusions. FIG. 9B shows a model of a beam having both ends fixed,which receives an even distributed load. FIG. 9C is a view forexplaining the relation between the substrate surface and a neutralplane not deformed by the flexure of the substrate.

[0093] Where the spacing between protrusions 2 for supporting thesubstrate is 1, the flexure of the substrate is such as shown in FIG.9A. In this case, as regards a material dynamic model, a model of a beamhaving both ends fixed and receiving an even distributed load such asshown in FIG. 9B applies. According to “Mechanical EngineeringHandbook”, edited by Japanese Mechanical Engineering Association,Maruzen Co., if a load per a unit length as determined by a vacuumpressure p or the like is w, a sectional secondary moment is I, thespacing between the protrusions is 1, and a longitudinal elasticitycoefficient is E, then the flexure v of the substrate at a position xwith respect to a direction from a protrusion end as an origin to ajuxtaposed protrusion as well as the inclination i of the substrate areexpressed as follows:

v=(wl ⁴/24EI)[x ² /l ²−2x ³ /l ³ +x ⁴ /l ⁴]  (1.1)

i=(wl ³/12EI)[x/l−3x ² /l ²+2x ³ /l ³]  (1.2)

[0094] Here, when a thickness h of the substrate and a width b thereofshown in FIG. 9B are used, it follows that there are relations such asfollows:

I=bh ³/12  (1.3)

w=pb  (1.4)

[0095] In FIG. 9C, a dash-and-dot line passing about the center of thethickness h depicts a neutral plane which is not elongated or contractedin X direction, at any x position thereof. With respect to this neutralplane, depending on the location there occurs an elongation/contractionin X direction of the substrate surface. Since the distance from theneutral plane to the substrate surface is influenced by the processingstate of the substrate or the attraction state thereof, taking k as aneutral plane correction coefficient, the coordinate error d of thesubstrate surface can be expressed as follows:

d=k(hi/2)=k(hwl ³/24EI)[x/l−3x ² /l ²+2x ³ /l ³]  (1.5)

[0096] From this, it follows that:

d=f(x)=k(pl ³/2h ² E)[x/l−3x ² /l ²+2x ³ /l ³]  (1.6)

[0097] The tolerance for the alignment error (i.e., the differencebetween the value x in an idealistic state and the value xa beingshifted practically) between the disposition of the alignment mark ofthe substrate and the disposition of the protrusion of the chuck, if atolerance for the coordinate error not adversely influential to thealignment is set, can be detected from equation (1.6) above, since thevalues p, h, E and I are known as determined by the apparatus or thesubstrate to be used in practice. If the tolerance for the coordinateerror is denoted by d_(c), then the alignment error tolerance x_(c) canbe determined to satisfy equation (1.7) below:

d _(c) ≧f(x _(c))−f(x ₀)  (1.7)

[0098] Practically, while the two-dimensional disposition of theprotrusions is taken into account, equation (1.6) as the same isadvanced may be used, with a result of a higher accuracy.

[0099] Referring to FIG. 10, a mechanism for changing substrates andchucks in accordance with the present invention will now be described.

[0100] In the present invention, when the disposition of the alignmentmark of the substrate is changed and, as a result, the predeterminedpositional relation with the disposition of the protrusions of the chuckis changed, the chuck has to be replaced by another. FIG. 10 shows amechanism for changing chucks without decreasing the throughput.

[0101] In FIG. 10, denoted at 116 is a chuck cassette for accommodatingtherein plural chucks 1 a, 1 b, . . . , each having protrusions disposedin accordance with the processing shape for substrates. Denoted at 117is a conveyance robot for unloading a desired chuck from the chuckcassette 116 and for conveying the same onto a chuck stage 107 on whichan exposure process or the like is to be performed. Denoted at 123 is asubstrate cassette for accommodating therein plural substrates to beprocessed. Denoted at 124 is another conveyance robot for unloading eachsubstrate 100 from the substrate cassette 123 and for conveying the sameonto a prealignment stage 125. Denoted at 127 is a conveyance robot formoving a substrate, having been prealigned by the prealignment stage 125onto the chuck 1 already mounted on the X-Y stage 107.

[0102] With the structure of the mechanism described above, a substrate100 to be processed is taken out of the substrate cassette 123 by theconveyance robot 124. Generally, it is placed on the prealignment stage125 having an outer peripheral shape detecting sensor 126 for thesubstrate, and a rough alignment operation of the same with respect to aprojected image in an exposure apparatus is performed there. During thisprealignment operation, the chuck is replaced by a necessary chuck 1 bymeans of the chuck conveyance robot 117 and between the chuck stage 107and the chuck cassette 116. This enables use of a chuck suited to thesubstrate, without a large decrease of the throughput.

[0103] It is to be noted here that the substrate attracting and holdingmethod and the substrate attracting and holding system of the presentinvention are not limited to use in an exposure apparatus. They may ofcourse be used in a liquid crystal substrate manufacturing apparatus, amagnetic head manufacturing apparatus, various inspection machines for asemiconductor, or the manufacture of micro-machines, for example.

[0104] In accordance with the present invention as describedhereinbefore, the position of an alignment mark of a substrate or theposition where an alignment mark is going to be formed can be set at aspecific location in relation to flexure of a substrate to be attractedand held, to thereby avoid an adverse influence of a coordinate error ofthe alignment error due to flexure of the substrate surface. Further,the coordinate error of the alignment mark can be calculated beforehandfrom the positional relationship between the alignment mark and thedisposition of an protrusion for supporting the substrate adjacentthere. On the basis of the result of calculation, the coordinate errorof the alignment mark can be corrected.

[0105] Thus, in an exposure apparatus, degradation of the patternoverlay precision due to the influence of surface flexure, for example,of the substrate caused by the attraction and holding of the same, canbe avoided, and production of a defect of a semiconductor deviceresulting from the shape of the substrate surface can be prevented.

[0106] [Seventh Embodiment]

[0107] Next, a substrate attracting and holding system according toanother embodiment of the present invention will be described.

[0108]FIGS. 11A and 11B show an embodiment of a substrate attracting andholding system according to the present invention, wherein FIG. 11A is aplan view and FIG. 11B is a fragmentary sectional view thereof. FIG. 12is a plane showing a further embodiment of a substrate attracting andholding system of the present invention.

[0109] In FIGS. 11A and 11B, denoted at 301 is a chuck (substrateattracting and holding system) to be mounted on an X-Y stage of asemiconductor exposure apparatus, for example. The chuck has asupporting surface on which a substrate such as a wafer is to be placed,and the supporting surface is provided by a plurality of pin-likeprotrusions 310, 313 and 314 (which will hereinafter be referred to alsoas a “pin”) for supporting a substrate. The free top end of eachprotrusion is finished into a super flat face by a high-precisionlapping process.

[0110] The pin-like protrusions 310 shown in FIGS. 11A and 11B have apin diameter of 0.2 mm, and they are juxtaposed in a grid-like arraywith a disposition pitch of L mm. There is at least one suction hole 311for vacuum attraction, at the top face of the chuck, which iscommunicated with a vacuum source. In place of the grid-like dispositionof the pin-like protrusions 310, they may be arrayed concentrically asshown in FIG. 12. They may be disposed in a 60-deg. staggering array, orthey may be disposed at random with a pin pitch of L mm or less. Anarray based on combination of those described above may be used.

[0111] At the outer peripheral portion of the chuck 1, there are aplurality of pin-like (outer peripheral) protrusions 313 disposed in acircumferential shape, for supporting the outer peripheral portion of asubstrate. Also, there is a ring-like partition wall 312 just inside theouter peripheral protrusions 313. The ring-like partition wall 312 has aheight which is lower than the top face of the protrusions 313 by about1 to 2 microns. This is because, with a gap of about 1-2 microns, adecrease of vacuum pressure for attraction is so small that it causes noproblem. On the other hand, even if a dust particle of a diametersmaller than the difference of 1-2 microns is adhered to the partitionwall 312, it does not contact the substrate. Thus, it does not cause anincrease of the contract rate. In FIGS. 11A and 11B, denoted at 314 areprotrusions disposed along a circumference inside the outermostprotrusions 313 by one pitch, and they are disposed in juxtaposition tothe inside face of the ring-like partition wall 312.

[0112] With the structure of the chuck 1 described above, the substrate302 such as a wafer is placed on the supporting surface of the chuckand, through vacuum suction applied in response to the operation of thevacuum source via the suction holes 311, the substrate 302 is supportedon the chuck and attracted and held by the protrusions 310, 313 and 314as shown in FIG. 13 or 19. Here, between the protrusions, the wafer(substrate) 2 is deformed and flexed by the vacuum attraction force, andthe flatness of the wafer is degraded. Also, due to the flexure of thewafer, the wafer surface is distorted in horizontal directions to causea positional deviation and thus a wafer distortion.

[0113] Now, the wafer flatness and the amount of wafer distortion willbe considered, using a material dynamics model.

[0114]FIG. 13 is a sectional view showing the flexure at the portion ofa wafer 302 where, in the central portion of the chuck 301, there arepin-like protrusions 310 juxtaposed continuously along one directionwith a pin pitch L, when the wafer is attracted and held thereby. Inthis example, as regards a material dynamics model, a model of a beamhaving its opposite ends fixed and receiving an even distributed load,as shown in FIG. 14, applies.

[0115] Here, if the width of the beam is b, the thickness thereof is h,and the sectional secondary moment is I, it follows that:

I=(b·h ³)/12  (2.1)

[0116] If the vacuum pressure is p and the load per a unit length is w,it follows that:

w=p·b  (2.2)

[0117] Where the length of the beam is L and the longitudinal elasticitycoefficient is E, the maximum flexure amount v of the beam is given by:

v=(w·L ⁴)/(384·E·I)  (2.3)

[0118] By modifying equation (2.3) by using equations (2.1) and (2.2),it follows that:

v=(P·L ⁴)/(32·E·h ³)  (2.4)

[0119] Namely, this means that the largest flexure amount v of the beamis not dependent upon the width b but, rather, it is determined by thevacuum pressure p, the beam length L, the longitudinal elasticitycoefficient E and the thickness h. Then, the largest flexure amount vcorresponds to the wafer flatness.

[0120] Next, where the coordinate of the beam in its lengthwisedirection is x and the bending moment is M, it follow that:

M=(w·L ²/2)[−1/6+x/L−x ² /L ²]  (2.5)

[0121]FIG. 15 shows the relation (curve 15) between the coordinate x andthe moment M as well as the flexure curve (curve 16) of the beam. Asseen also from FIG. 15, the moment M is negative in ranges a and c ofthe coordinate x, whereas it is positive in a range b. Also, at twopositions x1 and x2 where M becomes equal to zero, the tilt angle of thebeam flexure curve becomes largest. Where this largest tilt angle isdenoted by α, it follows that:

α=({square root}{square root over (3)}w·L ³)/(216·E·I)  (2.6)

[0122] When this is modified by using equations (2.1) and (2.2), itfollows that:

α=({square root}{square root over (3)}·P·L ³)/(18·E·h ³)  (2.7)

[0123] Since in practice a wafer has a thickness h, if it is illustratedwith exaggeration, the result is such as shown in FIG. 16. In FIG. 16, adash-and-dot line 17 passing through the middle of the thickness hdepicts a neutral plane at any position on which there occurs noelongation or contraction. At a side of the neutral plane facing thewafer surface, due to the bending moment M, there occurs an elongation,by tension, in X direction within the ranges a and c of the coordinatesx. In the range b, there occurs a contraction in X direction, bycompression. On the other hand, at a side of the neutral plane facingthe wafer bottom surface, there occurs a contraction, by compression, inthe ranges a and c of the coordinate x, while there occurs an elongationin X direction, by tension, in the range b. The amount of elongation orcontraction in the X direction is proportional to the distance from theneutral plane and also, it is proportional to the tilt angle of theneutral plane. Namely, a positional deviation to be produced by theelongation/contraction of the wafer surface in the X direction resultingfrom the attraction, becomes equal to zero at the positions x3, x5 andx7 where the tilt angle is zero, whereas it becomes largest at thepositions x4 and x6 where the tilt angle is maximum. As regards thedistance from the neutral plane to the wafer surface, in a case of amonocrystal Si wafer, it may be approximately equal to h/2. However, itmay differ from h/2, depending on the material or uniformess of thewafer or the substrate, the process or processes having been applied tothe surface or bottom surface, the state of attraction to the chuck, forexample. Thus, by taking it as k·h/2 wherein k is the neutral planecorrection coefficient and if the largest positional deviation isdenoted by u, it follows that:

u=[(h·α)/2]·k  (2.8)

[0124] When this is modified by using equation (2.7), it follows that:

u=[({square root}{square root over (3)}·P·L ³)/(36·E·h ²)]·k  (2.9)

[0125] Namely, this means that the largest positional deviation amount uon the wafer surface is not dependent upon the width b but, rather, itis determined by the neutral plane correction coefficient k, the vacuumpressure p, the beam length L, the longitudinal elasticity coefficient Eand the thickness h. Since the exposure process is performed in thisstate, the image to be printed on the wafer is an image being distortedrelatively to the wafer by an amount corresponding to the positionaldeviation. Therefore, the largest positional deviation u corresponds tothe wafer distortion.

[0126] While the explanation above has been made to a one-dimensionalbeam model in respect to the portion where the pin-like protrusions 310are juxtaposed continuously along one direction with a pin pitch L,practically the pin array comprises a two-dimensional array. Dependingon the disposition used, such as grid-like disposition, circumferentialdisposition, 60-deg. staggering disposition, random disposition or thelike, the values of the largest flexure amount v and the largestpositional deviation u are variable. In consideration of it, where thewafer flatness as a flat wafer is attracted in practice is V₁, the waferdistortion is U₁ and the correction coefficients depending on the pindisposition are c₁ and c₂, it follows that:

V ₁ =v·c ₁=[(P·L ⁴)/(32·E·h ³)]·c ₁  (2.10)

U ₁ =u·c ₂=[({square root}{square root over (3)}·P·L ³)/(36·E·h ²)]·k·c₂  (2.11)

[0127] In the case of grid-like disposition, as shown in FIG. 17, sincethe largest flexure occurs at the position of the center 318 of fourpins 319-323, it can be regarded that the flexure becomes larger thanthat of a case where a beam 323 supported by the pins 319 and 323 isconsidered and the flexure is calculated while taking the length as L,and also that it becomes smaller than that of a case where a beam 324 assupported by diagonal protrusions 319 and 321, of the four pins, isconsidered and the flexure is calculated while taking the length asL·2^(1/2). Therefore, it can be regarded that the correction coefficientc₁ becomes equal to 1 to 4 (=(2^(1/2))⁴) while the correctioncoefficient c₂ becomes equal to 1 to 2.8 (=(2^(1/2))³). Since howeverthe beam 324 supported by the diagonal pins 319 and 321 and the beam 325supported by the diagonal pins 320 and 322 may be flexed independently,by the same amount, the value may be close to that as determined whiletaking the beam length as L·2^(1/2).

[0128] On the other hand, in the case of 60-deg. staggering disposition,as shown in FIG. 18, the largest flexure occurs at the position of thecenter 326 of three pins. Therefore, it can be regarded that the flexurebecomes larger than that of a case where a beam 331 supported by thepins 327 and 331 is considered and the flexure is calculated whiletaking the length as L, and also that it becomes smaller than that of acase where a beam 333 passing through the center 326 of the three pinsand being supported by pins 327 and 328 is considered and the flexure iscalculated while taking the length as L·2/3^(1/2). Therefore, it can beregarded that the correction coefficient c₁ becomes equal to 1 to 1.8(=(2/3^(1/2))⁴) while the correction coefficient c₂ becomes equal to 1to 1.5 (=(2/3^(1/2))³).

[0129] Further, in the case of circumferential disposition or randomdisposition, it may be considered as a modification of the grid-likedisposition or the 60-deg. staggering disposition. Depending on thedegree of modification, the values of the correction coefficients arechanged. However, with a small modification, it can be regardedsubstantially the same as the grid-like disposition or the 60-deg.staggering disposition. The correction coefficients may be of the samevalues.

[0130] In practice, the correction coefficients c₁ and c₂ may becalculated on the basis of FEM, for each of different poi dispositions,by which they can be determined more accurately. Further, the correctioncoefficient c₁ or k·c₂ may be evaluated on the basis of experiments, bywhich it can be determined more accurately.

[0131] Since the wafer flatness V₁ and the wafer distortion U₁ as a flatwafer is attracted in practice are expressed by equations (2.10) and(2.11), if a wafer flatness tolerance as being tolerable in a chuck isdz and similarly the wafer distortion tolerance is dxdy, it followsthat:

dz≧[(P·L ⁴)/(32·E·h ³)]·c ₁  (2.12)

dxdy≧[({square root}{square root over (3)}·P·L ³)/(36·E·h ²)]·k·c₂  (2.13)

[0132] Here, once a wafer (substrate) to be attracted is determined,then the longitudinal elasticity coefficient E, the thickness h and theneutral plane correction coefficient k are determined. If the pin(protrusion) disposition is fixed, the correction coefficients c₁ and c₂based on the pin disposition are determined. Therefore, a suitablecombination of a vacuum pressure P and a pin pitch L, satisfying theconditions of equations (2.12) and (2.13), can be selected.

[0133] Namely, when equations (2.12) and (2.13) are modified, it followsthat:

P≦[(32·E·h ³ ·dz)/c ₁]·(1/L ⁴)  (2.14)

P≦[(36·E·h ² ·dxdy)/({square root}{square root over (3)}·k·c ₂)]·(1/L³)  (2.15)

[0134] Thus, by arranging the chuck with a vacuum pressure P and a pinpitch L, satisfying both of equations (2.14) and (2.15), the waferflatness and the distortion can be made smaller than the tolerances dzand dxdy, respectively.

[0135] On the other hand, as regards these two conditions, if the pinpitch L is not greater than a certain value and as long as the conditionof equation (2.15) is satisfied, the condition of equation (2.14) isalso satisfied. This value for the pitch L can be determined under acondition that the right side of equation (2.15) is smaller than theright side of equation (2.14), and it is given as follows:

L≦[(8·{square root}{square root over (3)}·k·c ₂)/(9·c₁)]·[(h·dz)/dxdy]  (2.16)

[0136] Namely, within the range in which the pin pitch L satisfiesequation (2.16), a chuck with a vacuum pressure P and a pin pitch Lsatisfying equation (2.15) may be used.

[0137] Thus, now a case wherein a typical Si wafer of a diameter 200 mmis attracted and held by a pin chuck having a grid-like pin dispositionis considered. It is taken that the longitudinal elasticity coefficientE=1.69×10¹¹ N/m, the thickness h=0.725 mm, the neutral plane correctioncoefficient k=1, the correction coefficients c₁=4 and c₂=2.8. Also, in asemiconductor process of 0.25 micron rule, currently beingmass-produced, the wafer flatness tolerance dz is 80 nm, when taken as10% of the depth of focus 800 nm. The wafer distortion tolerance dxdy is5 nm, when taken as 10% of the overlay precision 50 nm. Then, whiletaking the unit of pressure P is N/m² and the unit of pitch L is m, fromequations (2.15) and (2.16), it follows that:

P≦0.0033/L³  (2.17)

L≦0.0125  (2.18)

[0138] It is seen that, when the pin pitch L is not greater than 12.5mm, a vacuum pressure P and a pin pitch L satisfying equation (2.17) maybe used. Since, generally, the pin pitch L is not greater than 5 mm, tobe described later, it applies to that.

[0139] Here, it should be noted that, in the normal pin pitch,satisfaction of only equation (2.15) is accompanied by satisfaction ofequation (2.14) means that there is a more strict condition involved inreducing the wafer distortion to a tolerance or smaller; as comparedwith improving the wafer flatness. In order to clarify this, the ratioof the wafer flatness V₁ and the wafer distortion U₁ may be detectedfrom equations (2.10) and (2.11). If follows that:

V ₁ /U ₁=[(9·c ₁)/(8·{square root}{square root over (3)}·k·c₂)]·(L/h)  (2.19)

[0140] By substituting typical coefficients similar to those describedabove, into this equation, it follows that:

V ₁ /U ₁=1280·L  (2.20)

[0141] This means that, if the pin pitch L is 2 mm, for example, thereoccurs a wafer distortion U₁ corresponding to {fraction (1/2.6)} of thewafer flatness V₁. Namely, it means that, if the tolerance for the waferdistortion is 5 nm, only a wafer flatness of 13 nm is allowed. Thisvalue is extraordinarily strict as compared with the wafer flatnesstolerance of 80 nm, determined by the depth of focus. Also, if the pinpitch L is large, the rate of wafer distortion production relative tothe wafer flatness becomes small. It can not reach the rate of waferdistortion tolerance relative to the wafer flatness tolerance, unless apin pitch L is set to 12.5 mm.

[0142] Next, referring to FIG. 25, the range of practical values for thevacuum pressure P and the pin pitch L will be described. FIG. 25 is agraph wherein the pin pitch L is taken on the axis of abscissa, and thevacuum pressure P is taken on the axis of ordinate. The range for thevacuum pressure P and the pin pitch L satisfying equation (2.17) is atthe lower left zone of a solid line 342.

[0143] Although equation (2.17) has been determined with reference to aSi wafer of a diameter 200 mm, having a thickness h=0.725 mm, a Si waferof a diameter 125 mm may have a thickness h=0.725 mm and, in thatoccasion, it follows that:

P≦0.00245/L ³  (2.21)

[0144] Thus, in FIG. 25, the range corresponds to a lower left zonebelow a solid line 343.

[0145] Further, for a Si wafer of 300 mm diameter, the thickness ish=0.775 mm. Also, it is expected that wafers of a larger diameter suchas 400 mm Si wafers are used in future. The thickness will be comeh=about 0.825 mm. In consideration of this, the value is calculated witha thickness h=0.825 mm. Then, it follows that:

P≦0.00427/L ³  (2.22)

[0146] In FIG. 25, it corresponds to a lower left zone below a solidline 341.

[0147] Further, with further miniaturization of a semiconductor device,the semiconductor process will change to 0.18 micron rule, 0.13 micronrule or to 0.1 micron rule. With these changes, improvements in theoverlay precision are absolutely required. Thus, it is expected that thetolerance for wafer distortion is changed to a much strict value, suchas from 5 nm to 2.5 nm and to 1 nm.

[0148] In consideration of the above, the value is calculated on thebasis of a wafer distortion tolerance dxdy=2.5 nm and a thicknessh=0.825 mm. It follows that:

P≦0.00213/L ³  (2.23)

[0149] In FIG. 25, it corresponds to a lower left zone below a solidline 344.

[0150] Similarly, when the value is calculated with a wafer distortiontolerance dxdy=2.5 nm and a thickness h=0.725 mm, it follows that:

P≦0.00165/L ³  (2.24)

[0151] In FIG. 25, it corresponds to a lower left zone below a solidline 345.

[0152] Similarly, when the value is calculated with a wafer distortiontolerance dxdy=2.5 nm and a thickness h=0.625 mm, it follows that:

P≦0.00123/L ³  (2.25)

[0153] In FIG. 25, it corresponds to a lower left zone below a solidline 346.

[0154] Further, when the value is calculated with a wafer distortiontolerance dxdy=1 nm and a thickness h=0.825 mm, it follows that:

P≦0.00085/L ³  (2.26)

[0155] In FIG. 25, it corresponds to a lower left zone below a solidline 347.

[0156] Similarly, when the value is calculated with a wafer distortiontolerance dxdy=1 nm and a thickness h=0.725 mm, it follows that:

P≦0.00066/L ³  (2.27)

[0157] In FIG. 25, it corresponds to a lower left zone below a solidline 348.

[0158] Similarly, when the value is calculated with a wafer distortiontolerance dxdy=1 nm and a thickness h=0.625 mm, it follows that:

P≦0.00049/L ³  (2.28)

[0159] In FIG. 25, it corresponds to a lower left zone below a solidline 349.

[0160] As described above, the practical range for the vacuum pressure Pand the pin pitch L at the wafer central portion has been considered inaccordance with equation (2.15) and in respect to various values of thewafer thickness h and the wafer distortion tolerance dxdy. In theseexamples, since the range of the pin pitch L as determined by equation(2.16) satisfies a standard pin pitch (not greater than 5 mm) to bedescribed later, the condition of equation (2.14) is also satisfied.This is because, even in a case where the right side of equation (2.16)becomes smallest, that is, even in the case of a smallest thicknessh=0.625 mm and a largest dxdy=5 nm, a relation L≦0.011 is given suchthat the standard pin pitch 5 mm to be described later is satisfied.Therefore, by arranging the chuck with a vacuum pressure P and a pinpitch L, at the wafer central portion, which are selected out of therange described above, a desired wafer flatness tolerance dz and adesired wafer distortion tolerance dxdy can be satisfied.

[0161] The ordinary range for the vacuum pressure P of the chuck willbe, under different conditions of the chuck, as follows. First, thesmallest vacuum pressure which can be used in practice, is determined bythe condition for holding a wafer even if an X-Y stage for holding thechuck moves at a largest acceleration. Namely, if the largestacceleration of the X-Y stage is G, the stationary friction coefficientis μ, the wafer area of (s), the wafer density is ρ, then it followsthat:

P·(s)·μ≧G·(s)·h·ρ  (2.29)

[0162] Namely, it follows that:

P≧G·h·ρ/μ  (2.30)

[0163] Here, if the largest acceleration of the X-Y stage G=0.2×9.8=1.96m/s², the stationary friction coefficient μ=0.1, the thickness h=0.625mm, the wafer density ρ=2330 Kg/m², then it follows that:

P≧33  (2.31)

[0164] In FIG. 25, it corresponds to an upper zone above a solid line350.

[0165] Next, the largest vacuum pressure P which can be used in practiceis, if the atmospheric pressure is 100 kN/m², as follows:

P≦100000  (2.32)

[0166] In FIG. 25, it corresponds to a lower zone below a solid line351.

[0167] On the other hand, an ordinary range for the pin pitch L of thechuck will be, under different conditions of the chuck, as follows. Thesmallest pin pitch L which can be used in practice is determined by thecontact rate between the chuck and the wafer. Therefore, the relationbetween the pin pitch and the contact rate will be described first. Ifthe number of pins per a unit area is n, since in the grid-likedisposition shown in FIG. 7, there is one pin in the area as enclosed bythe centers of the four pins 319-322, it follows that:

n=1/L ²  (2.33)

[0168] Further, in the case of the 60-deg. staggering disposition shownin FIG. 18, th re is one pin in the area as enclosed by four pins327-330, it follows that:

n(2/3^(1/2))/L²  (2.34)

[0169] Further, where the area at the free end of each pin is denoted bys and the wafer-to-pin contact rate is denoted by N, since N=s·n, itfollows that:

[0170] In the case of grid-like disposition:

N=s/L ²  (2.35)

[0171] In the case of 60-deg. staggering disposition:

N=(2/3^(1/2))·s/L ²  (2.36)

[0172] Therefore, the wafer-to-pin contact rate N is determined by thearea s at the free end face of the pin and the pin pitch L. According toexperiences of semiconductor processes, the practical contact rate N isabout 0.008 in a case where the pin pitch L is about 2 mm, and the pinfree end face has a diameter 0.2 mm, namely, the area s of the free endface of the pin is s=π·(0.1)²=0.0314 mm². Thus, by machining the pinfree end face to a diameter of about 0.05 mm, the pin pitch L can bereduced to 0.5 mm while keeping the contact rate of substantially thesame level. Thus, it follows that:

L≧0.0005  (2.37)

[0173] In FIG. 25, it corresponds to a right-hand side zone of a solidline 352.

[0174] Next, the largest pin pitch L which can be used in practice isdetermined by the periodicity of a local warp of the wafer. In practice,a wafer has various warps of different periodicities, such as those froma global warp extending throughout the wafer to a warp having a veryfine periodicity. It is an important function of a wafer chuck tocorrect these warps to accomplish the flatness. However, with a pinchuck, it is in principle unable to correct a warp having a periodicitysmaller than the pin pitch. Namely, it is necessary to make the pinpitch smaller than the smallest periodicity of a warp, of an amplitudeof about 13 nm, which may have an adverse influence as a waferdistortion. In order to accomplish a positive correction effect, a pinpitch not greater than a half of the smallest periodicity has to beused. As regards the periodicity of a wafer warp, while details are notknown because of difficulties in separation from the thicknessnon-uniformess or of the measuring precision, it should be expected thata warp of a period of about 10 mm at the largest may remain though thewafer warp may be improved in future. In consideration of it, the pinpitch should desirably be set to be 5 mm or less.

L≦0.005  (2.38)

[0175] In FIG. 25, it corresponds to a zone on the left-hand side of asolid line 353.

[0176] It is seen from the above that the practical range for the vacuumpressure P and the pin pitch L are determined in accordance withequations (2.22), (2.31), (2.32), (2.37) and (2.38), as follows:

P≦0.00427/L³

33≦P≦100000

0.0005≦L≦0.005  (2.39)

[0177] In FIG. 25, it corresponds to the range as enclosed by solidlines 341, 351, 352, 350 and 353.

[0178] While the foregoing description has been made with reference tothe portion where the pin-like protrusions 310 are juxtaposedcontinuously along one direction with a pin pitch L, that is, thecentral portion of the chuck inside the outer peripheral portionthereof, description will now be made on the outer peripheral portion ofthe chuck. FIG. 19 is a sectional view for explaining flexure of a wafer2 as attracted and held by the outer peripheral potion of the chuck. Inthis drawing, the partition wall 312 is provided just inside theoutermost circumferential protrusion 313, and the height of thepartition wall 312 is made lower than the top face of the protrusion 313by about 1-2 microns. This is because, with a gap of about 1-2 microns,a decrease of vacuum pressure for attraction is so small that it causesno problem. On the other hand, even if a dust particle of a diametersmaller than the difference of 1-2 microns is adhered to the partitionwall 312, it does not contact the substrate. Thus, it does not cause anincrease of the contract rate.

[0179] As regards a material dynamics model for the state of flexure ofa wafer at the outer peripheral portion of the chuck, a model of a beamhaving a fixed end and another free end and receiving a even distributedload, as shown in FIG. 20, applies. However, the outermostcircumferential pin 313 supports a wafer 302 with its corner, not thecenter of the pin, as shown in FIG. 19. The pin pitch L in this case isthe distance from the inside corner of the pin 313 to the pin 314 whichis located inside thereof by one pitch.

[0180] Where the maximum flexure amount is denoted by v, it is expressedas follows:

v=(w·L ⁴)/(184.6·E·I)  (2.40)

[0181] By modifying this equation by using equations (2.1) and (2.2), itfollows that:

v=(P·L ⁴)/(15.38·E·h ³)  (2.41)

[0182] Also, the tilt angle of the beam flexure curve becomes largest atthe supporting position of the outermost pin 313. If this largest tiltangle is denoted by α, it follows that:

α=(w·L ³)/(48·E·I)  (2.42)

[0183] When this is modified by using equations (2.1) and (2.2), itfollows that:

α=(P·L ³)/(4·E·h ³)  (2.43)

[0184] Thus, from equation (2.8), the largest positional deviation u isgive as follows:

u=[(P·L ³)/(8·E·h ²)]·k  (2.44)

[0185] Therefore, where the wafer flatness as a flat wafer is attractedin practice is V₂, the wafer distortion is U₂ and the correctioncoefficients depending on the pin disposition, like those of the wafercentral portion, are c₁ and c₂, it follows that:

V ₂ =v·c ₁=[(P·L ⁴)/(15.38·E·h ³)]·c ₁  (2.45)

U ₂ =u·c ₂=[(P·L ³)/(8·E·h ²)]·k·c ₂  (2.46)

[0186] Since the wafer flatness V₁ and the wafer distortion U₁ as a flatwafer is attracted in practice are expressed by equations (2.10) and(2.11), also in the case of the wafer outer peripheral portion, if awafer flatness tolerance as being tolerable in a chuck is dz andsimilarly the wafer distortion tolerance is dxdy, it follows that:

dz≧[(P·L ⁴)/(15.38·E·h ³)]·c ₁  (2.47)

dxdy≧[(P·L ³)/(8·E·h ²)]·k·c ₂  (2.48)

[0187] When equations (2.47) and (2.48) are modified, it follows that:

P≦[(15.38·E·h ³ ·dz)/c ₁]·(1/L ⁴)  (2.49)

P≦[(8·E·h ² ·dxdy)/(k·c ₂)]·(1/L ³)  (2.50)

[0188] Thus, by arranging the chuck with a vacuum pressure P and a pinpitch L, satisfying both of equations (2.49) and (2.50), the waferflatness and the distortion can be made smaller than the tolerances dzand dxdy, respectively.

[0189] On the other hand, as regards these two conditions, if the pinpitch L is not greater than a certain value and as long as the conditionof equation (2.50) is satisfied, the condition of equation (2.49) isalso satisfied. This value for the pitch L can be determined under acondition that the right side of equation (2.50) is smaller than theright side of equation (2.49), and it is given as follows:

L≦[(1.92·k·c ₂)/c ₁]·[(h·dz)/dxdy]  (2.51)

[0190] Namely, within the range in which the pin pitch L satisfiesequation (2.51), a chuck with a vacuum pressure P and a pin pitch Lsatisfying equation (2.50) may be used.

[0191] Thus, now a case wherein a typical Si wafer of a diameter 200 mmis attracted and held by a pin chuck having a grid-like pin dispositionis considered, like the example of the wafer central portion describedhereinbefore. It is taken that the longitudinal elasticity coefficientE=1.69×10¹¹ N/m, the thickness h=0.725 mm, the neutral plane correctioncoefficient k=1, the correction coefficients c₁=4 and c₂=2.8. Also, in asemiconductor process of 0.25 micron rule, the wafer flatness tolerancedz is 80 nm and the wafer distortion tolerance dxdy is 5 nm. Then, whiletaking the unit of pressure P is N/m² and the unit of pitch L is m, fromequations (2.50), it follows that:

P≦0.0127/L ³  (2.52)

[0192]FIG. 26 is a graph for explaining the range for the vacuumpressure P and the pin pitch L which can be used in practice, whereinthe pin pitch L is taken on the axis of abscissa, and the vacuumpressure P is taken on the axis of ordinate. In FIG. 26, the range forthe vacuum pressure P and the pin pitch L satisfying equation (2.52) isat the lower left zone below a solid line 362.

[0193] When the range is calculated with a thickness h=0.626 mm, itfollows that:

P≦0.00094/L ³  (2.53)

[0194] Thus, in FIG. 26, the range corresponds to a lower left zonebelow a solid line 363.

[0195] Similarly, when the range is calculated for a thickness h=0.825mm, it follows that:

P≦0.00164/L ³  (2.54)

[0196] In FIG. 26, it corresponds to a lower left zone below a solidline 361.

[0197] Also, when the range is calculated for a wafer distortiontolerance dxdy=2.5 nm and a thickness h=0.825 mm, it follows that:

P≦0.00082/L ³  (2.55)

[0198] In FIG. 26, it corresponds to a lower left zone below a solidline 364.

[0199] Similarly, when the range is calculated for dxdy=2.5 nm andh=0.725 mm, it follows that:

P≦0.00063/L ³  (2.56)

[0200] In FIG. 26, it corresponds to a lower left zone below a solidline 365.

[0201] Similarly, when the range is calculated for dxdy=2.5 nm andh=0.625 mm, it follows that:

P≦0.00047/L ³  (2.57)

[0202] In FIG. 26, it corresponds to a lower left zone below a solidline 366.

[0203] Also, when the range is calculated for dxdy=1 nm and h=0.825 mm,it follows that:

P≦0.00033/L ³  (2.58)

[0204] In FIG. 26, it corresponds to a lower left zone below a solidline 367.

[0205] Similarly, when the range is calculated for dxdy=1 nm and h=0.725mm, it follows that:

P≦0.00025/L ³  (2.59)

[0206] In FIG. 26, it corresponds to a lower left zone below a solidline 368.

[0207] Similarly, when the range is calculated for dxdy=1 nm and h=0.625mm, it follows that:

P≦0.00019/L ³  (2.60)

[0208] In FIG. 26, it corresponds to a lower left zone below a solidline 369.

[0209] As described above, the practical range for the vacuum pressure Pand the pin pitch L at the wafer outer peripheral portion has beenconsidered in accordance with equation (2.50) and in respect to variousvalues of the wafer thickness h and the wafer distortion tolerance dxdy.In these examples, since the range of the pin pitch L as determined byequation (2.51) satisfies a standard pin pitch (not greater than 5 mm)to be described later, the condition of equation (2.49) is alsosatisfied. This is because, even in a case where the right side ofequation (2.51) becomes smallest, that is, even in the case of asmallest thickness h=0.625 mm and a largest dxdy=5 nm, a relationL≦0.013 is given such that the standard pin pitch 5 mm to be describedlater is satisfied. Therefore, by arranging the chuck with a vacuumpressure P and a pin pitch L, also at the wafer outer peripheralportion, which are selected out of the range described above, a desiredwafer flatness tolerance dz and a desired wafer distortion tolerancedxdy can be satisfied.

[0210] Here, it should be noted that, in the normal pin pitch,satisfaction of only equation (2.50) is accompanied by satisfaction ofequation (2.49) means that there is a more strict condition involved inreducing the wafer distortion to a tolerance or smaller, as comparedwith improving the wafer flatness.

[0211] By the way, the ordinary range for the chuck vacuum pressure P isdefined by equations (2.31) and (2.32) like the case of the wafercentral portion, and in FIG. 26, it corresponds to a zone above a solidline 370 and a zone below a solid line 371.

[0212] On the other hand, the ordinary range for the pin pitch L of thechuck is defined by equations (2.37) and (2.38), like the case of thewafer central portion, and in FIG. 26, it corresponds to a zone on theright-hand side of a solid line 372 and a zone on the left-hand side ofa solid line 373.

[0213] It is seen from the above that the practical range for the vacuumpressure P and the pin pitch L are determined in accordance withequations (2.54), (2.31), (2.32), (2.37) and (2.38), as follows:

P≦0.00164/L ³

33≦P≦100000

0.0005≦L≦0.005  (2.61)

[0214] Thus, in FIG. 26, it is a zone as enclosed by solid lines 361,371, 372, 370 and 373.

[0215] As described above, because the wafer central portion and thewafer peripheral portion are different in respect to the manner ofsupporting the wafer, the chuck may be structured to have respectivevacuum pressures P and respective pin pitches L selected out of theranges described hereinbefore, by which a desired wafer flatnesstolerance dz and a desired wafer distortion tolerance dxdy can besatisfied throughout the whole wafer surface.

[0216] At the wafer central portion and the wafer peripheral portion, acommon vacuum pressure P and/or a common pin pitch L may be set, withinthe ranges described hereinbefore. Alternatively, they may be setindependently of each other. Where vacuum pressures P should be setindependently of each other, in addition to the outermost peripheralpartition wall 312, a continuous inside partition wall may be providedso as to connect all the pins 314 disposed circumferentially inside theoutermost pins 313 by one pitch, and vacuum suction opening bores may beformed in the wafer central portion and the wafer peripheral portion ofthe chuck such that vacuum pressures can be supplied to themindependently. Further, as regards the inner partition wall, a ring-likepartition wall 334 (FIG. 21) may be provided with a small inward shiftfrom the pin 314. This facilitates formation of a step at the innerpartition wall 334. The height of the inner partition wall shouldpreferably be made lower than the top face of the pin 314 by 1-2microns. This is because, in that structure, it does not contact a wafereven if the same is warped. Also, if a dust particle of a diametersmaller than that spacing is adhered, it does not contact the wafer. Thecontract rate is not raised.

[0217] Where the height of the inner partition wall is made lower thanthe top face of the pin 314 and a vacuum pressure is supplied only tothe wafer central portion, the vacuum pressure at the wafer peripheralportion can be made lower than that at the wafer central portion.Alternatively, an opening bore being communicated with the atmospheremay be formed in the wafer central portion, and a vacuum pressure may besupplied only to the wafer peripheral portion. In that occasion, thevacuum pressure at the wafer peripheral portion can be held higher thanthat at the wafer central portion. In this case, only a single vacuumsupplying line is necessary.

[0218] While the outermost partition wall 312 is disposed with a slightinward shift from the pin 313 as shown in FIG. 19 or 21, it may beprovided outside the pin 313. Alternatively, a continuous partition wallfor connecting all the pin 313 may be provided so as to surround thechuck peripheral portion. As a further alternative, while the contactrate becomes larger, the pins 313 may be omitted and, in place thereof,an outermost partition wall of the same height as the top face of thepin 313 may be provided.

[0219] Arranging the structure so that the vacuum pressure P can be setindependently at the wafer central portion and the wafer peripheralportion, as described above, enables that the vacuum pressure at thewafer central portion is set to assure that the wafer can be held evenif the X-Y stage moves at its maximum acceleration, for example, whilethe vacuum pressure at the wafer peripheral portion is set to assurethat even a wafer having a large warp throughout the whole wafer can beattracted. More specifically, by setting the vacuum pressure at thewafer peripheral portion higher than that at the wafer central portion,and by making the pin pitch narrow, the attraction of the wafer at thewafer peripheral portion can be assured regardless of thepresence/absence of a wafer warp. This enables good flatness correctionat the peripheral portion as well as good correction of the waferdistortion. The vacuum pressure at the wafer central portion may be keptat a lowest level for wafer holding, by which the pin pitch can be madelarge. This enables decreasing the contact rate.

[0220] Further, the same pin pitch may be set at the wafer centralportion and the wafer peripheral portion, while on the other hand, thevacuum pressure at the peripheral portion may be set appropriately lowerthan that at the wafer central portion. This enables setting the samedistortion amount at the wafer central portion and the peripheralportion, thus avoiding an increase of the contact rate.

[0221] The vacuum pressure at the peripheral portion may setappropriately lower than that at the wafer central portion and the pinpitch may be made narrow properly. This enables setting the samedistortion amount at the wafer central portion and the peripheralportion and, additionally, it leads to enlargement of the range in whichtheir distribution shapes are approximately registered. Details will beexplained with reference to FIGS. 27A and 27B. FIG. 27A shows a flexurecurve of a wafer between the pin pitch. The axis of ordinate shows theflexure amount V. FIG. 27B shows the shape of distribution of waferdistortion between the pin pitch. The axis of ordinate shows the waferdistortion u. In FIGS. 27A and 27B, the axis of abscissa depicts thewafer position x between or inside the pin pitch, with rightwarddirection corresponding to the wafer outward direction. In FIG. 27A,denoted at 380 is a flexure curve at the wafer central portion. Denotedat 381 is a flexure curve at the wafer peripheral portion where thevacuum pressure is made properly lower than that at the wafer centralportion and also the pin pitch is made properly narrow. Denoted at 382is a flexure curve corresponding to a conventional example wherein,while the vacuum pressure is held constant, the pin pitch is madeappropriately narrower than that at the wafer central portion. In FIG.27B, denoted at 383, 384 and 345 are distribution shapes of waferdistortions corresponding to the flexure curve 380, the flexure curve381 and the flexure curve 382, respectively.

[0222] It is seen from these drawings that, as regards the waferdistortion distribution shape, in the curves 382 and 385 of theconventional example, only in a narrow range a of the wafer position x,the shape is approximately registered. As compared therewith, in thecurves 383 and 384 of this embodiment, in a wide range b which is abouttwice of the range a, the shape is approximately registered. Thus, therange for registration is widened. Although there remains a region,outside the range b, in which the shape is not registered, since at anoutermost periphery of a wafer there is an invalid area of at leastabout 1 mm where no semiconductor device is formed, this does not causea particular problem provided that the pin pitch is not greater thanabout 2 mm. Since the wafer distortions produced at the wafer centralportion and the peripheral portion can have substantially the sameshape, as described above, if a chuck having the same pin dispositionfor every shot of a wafer to be exposed is used, it can be accomplishedthat a distortion of substantially the same distribution shape isproduced in every shot. In that occasion, an image to be printed onevery shot can be corrected in accordance with the distribution shape ofthe wafer distortion such as by driving or rotating an imaging lens or areticle or by correcting the reticle pattern position beforehand. As aresult, the overlay precision can be improved much more, throughout awide range including the wafer peripheral portion.

[0223] As regards the vacuum pressures at the wafer central portion andthe peripheral portion, preferably they should be kept at a desiredconstant level without being influenced by a variation in atmosphericpressure, for example. To this end, a precision regulator, for example,may be used to supply a constant vacuum pressure, or the vacuum pressersmay be detected and controlled to a constant level. Particularly, inthis case, it is desirable since a good reproducibility of the waferdistortion distribution shape is assured thereby.

[0224] It is to be noted that FIGS. 27A and 27B are based on thefollowing equations according to a material dynamics. First, the flexurecurve 380 at the wafer central portion is given by:

v=[(P·L ⁴)/(2·E·h ³)](x ² /L ²−2x ³ /L ³ +x ⁴ /L ⁴)  (2.62)

[0225] The flexure curves 382 and 382 at the wafer peripheral portionare given by:

v=[(Q·R ⁴)/(4·E·h ³)][−(R−x)/R+{3·(R−x)³ /R ³}−{2·(R−x)⁴ /R ⁴}]  (2.63)

[0226] Here, for the curve 381, Q=0.85·P and R=0.87·L. For the curve382, Q=P and R=0.83·L.

[0227] The distribution shape 383 of the wafer distortion correspondingto the flexure curve 380 is given by:

u=[(P·L ³)/(2·E·h ²)][x/L−(3·x ²)/L ²+(2·x ³)/L ³]  (2.64)

[0228] Also, the distribution shape of the wafer distortioncorresponding to the flexure curves 381 and 382 is given by:

u=[(Q·R ³)/(8·E·h ²)][−1+{9·(R−x)² }/R ²−{8·(R−x)³ }/R ³]  (2.65)

[0229] Here, for the curve 384, Q=0.85·P and R=0.87·L. For the curve385, Q=P and R=0.83·L.

[0230] On the other hand, due to the influence of a polishing processduring the wafer production or the influence of various processes duringthe semiconductor manufacture, there are cases wherein the periodicityof local warps on a wafer is different between the wafer central portionand the peripheral portion. Where the periodicity at the peripheralportion is longer than that at the wafer central portion, the pin pitchat the wafer peripheral portion may be made wider than that at the wafercentral portion. Also, the vacuum pressures may be set respectively andappropriately so as not produce wafer distortion. By doing so, thecontact rate at the wafer peripheral portion where a dust particle canbe relatively easily adhered, can be lowered.

[0231] Further, although the free end faces of the pin-like protrusionsconstituting the wafer carrying and supporting surface have beenexplained as a super flat surface, depending on the actual processingprecision, a very small tilt may be produced there. In that occasion,therefore, the pitch of the pins which support the wafer may not beexactly the same as the pin pitch L described hereinbefore. At the wafercentral portion, in a worst case, for example, as shown in FIG. 22, thefree end faces of the pins 310 and 336 may be tilted in oppositedirections. In that occasion, the pitch of the points contacting thewafer becomes equal to Lx which is larger than the pin pitch L by anamount corresponding to the pin diameter. Thus, in this case, the waferflatness and the distortion will become larger than V₁ and U₁ inequations (2.10) and (2.11). On the other hand, at the wafer peripheralportion, in a worst case, for example, as shown in FIG. 23, the free endfaces of the pins 313 and 314 may be tilted down toward the inside asillustrated. In that occasion, the pitch becomes equal to Ly which islarger than the pin pitch L by an amount 1.5 times the pin diameter.Therefore, in this case, the wafer flatness and the wafer distortionbecome larger than V₂ and U₂ in equations (2.45) and (2.46). In orderthat the wafer distortion satisfies its tolerance throughout the wholesurface, as described above, the remainder to be provided by subtractinga value 1.5 times the pin diameter from the pin pitch L determined asdescribed above may be taken as the actual pin pitch. However, in thatcase, the pin-to-wafer contact rate increases accordingly, and it isundesirable. Therefore, it is effective to process and provide a flatsurface without having a tilt that may cause an adverse influence, or toreduce the pin diameter as much as possible. Also, as shown in FIG. 24,the free end face of the pin may be formed into a spherical shape. Thisis substantially equivalent to an example wherein the pin diameter issubstantially equal to zero, and the contact rate can desirably bereduced very much. Further, the free end may be formed with a concaveface without having a tilt, although the machining is not very easy.

[0232] At the wafer outer peripheral portion as shown in FIG. 19, thewafer portion projecting outwardly beyond the outermost pins 313 mayprotrude upwardly due to the deformation between the pins 313 and 314 atthe peripheral portion. The wafer flatness and the wafer distortion inthis portion will be described. The tilt angle at the peripheral portionbecomes largest at the supporting position of the pin 313. This largesttilt angle α is expressed by equation (2.43) as described hereinbefore.In the range outside the supporting position of the pin 313, the largesttilt angle α is kept constantly. Therefore, the wafer distortion asdetermined by the largest tilt angle is held constant, without anyincrease. Thus, there is no problem in relation to the wafer distortion.However, if the amount of outward projection of the wafer is large,since it projects with the same largest tilt angle α, the amount of suchupward protruding has to be kept smaller than the tolerance dz for thewafer flatness. Therefore, when the amount of wafer extension is J, itfollows that:

dz≧J·α  (2.66)

[0233] Taking equation (2.43) and the correction coefficient c₂ with thepin disposition into account, it follows that:

J≦[(4·E·h ³)/(P·L ³ ·c ₂)]·dz  (2.67)

[0234] Although the right side of equation (2.67) above becomes smallestwhen P·L³ becomes largest, from equation (2.50), now it follows that:

P·L ³≦(8·E·h ² ·dxdy)/(k·c ₂)  (2.68)

[0235] Therefore, equation (2.67) can be rewritten as follows:

J≦(k·h·dz)/(2·dxdy)  (2.69)

[0236] Further, the right side of equation (2.69) above becomes smallestwhen the neutral plane correction coefficient k=1, the smallestthickness h=0.625 mm, the wafer flatness tolerance dz=80 nm, and thelargest wafer distortion tolerance dxdy=5 nm. Then, J≦0.005. Namely, inorder to satisfy the wafer flatness tolerance dz due to deformationinside the pin pitch, the wafer projection amount may be held to mm orless. In that occasion, there occurs no problem, even in considerationof the diameter of the outermost pin 313, the outside shape tolerance ofthe wafer, the position precision of the same as placed on the chuck,and the width of the partition 312 when the same is provided outside thepin 313. Thus, the condition for correcting the wafer warp at the outerperipheral portion is more strict and, in this respect, the pin 313 atthe outermost periphery of the chuck should desirably be disposed closeto the outer periphery of the wafer as much as possible.

[0237] Although in the forgoing description the pin pitch of the chuckis explained as L and, at the wafer central portion and the peripheralportion, the chuck has a vacuum pressure P and a pin pitch L selectedout of the above-described ranges, the pin pitch may of course be setseparately and independently at the wafer central portion and theperipheral portion. Further, it is not necessary that a uniform pitch isdefined in the wafer central portion or in the wafer peripheral portion.As long as it is within the above-described range is satisfied, anon-uniform pin pitch may be used.

[0238] The substrate to be held by the chuck is not limited to a Siwafer. For example, various substrates such as a gallium arsenic wafer,a composite adhesion wafer, a glass substrate, a liquid crystal panelsubstrate, and a reticle may be used. Further, as regards the outsideshape thereof, it may not be circular, and it may have a rectangularshape, for example. In that occasion, the outside shape of the chuck maybe changed in accordance with the outside shape of the substrate.

[0239] Further, while the chuck has been explained as a vacuumattraction type chuck, the present invention is not limited to it. Thechuck may comprise an electrostatic type chuck, or it may use acombination of a vacuum attraction type and an electrostatic type. Inthese cases, the vacuum pressure P in the above-described embodimentsmay be replaced by an attraction force of a different type or acombination of it with the vacuum pressure.

[0240] Although the chuck has been described with reference to a pinchuck, the present invention is applicable also to chucks havingdifferent shapes. For example, a ring-like chuck having concentricring-like recesses (suction grooves) and concentric ring-likeprotrusions for defining a wafer supporting surface, which arealternately formed, may be used. In that occasion, the pitch of thering-like protrusions in the radial direction may be regarded as the pinpitch L. At the wafer central portion and the outer peripheral portion,a vacuum pressure P and a pin pitch L as has been described withreference to the embodiments may be set there. Substantially the sameadvantageous results are attainable with it.

[0241] In accordance with the present invention, degradation of thewafer flatness and distortion due to a flexure of a substrate inside thepin pitch as the same is held, can be reduced remarkably. Therefore, inthe procedure for manufacture of very fine devices, the defect of devicecan be reduced and the yield rate can be improved significantly.

[0242] Referring now to FIG. 18, an exposure apparatus into which asubstrate attracting and holding system such as described above can beincorporated, will be explained.

[0243]FIG. 28 is a schematic view of a general structure of a reductionprojection exposure apparatus. As shown in the drawing, a reticle 402which is an original having a pattern to be transferred to a substrate402 such as a silicon wafer, for example, is mounted on a reticle stage401 through a reticle chuck. The reticle is illuminated with exposurelight directed thereto through an illumination optical system 403. Theexposure light passing through the reticle 402 is reduced in scale by aprojection optical system 405, to ⅕, and it is projected on thesubstrate 402 which is a workpiece to be processed. A chuck 1 which is asubstrate holding system for holding the substrate 402, as describedhereinbefore, is mounted on an X-Y stage 406 which is movable along ahorizontal plane. The substrate 402 has a thin coating of a resistmaterial (photosensitive material) applied thereto beforehand, whichmaterial produces a chemical reaction in response to irradiation withthe exposure light. It functions as an etching mask in a subsequentprocess. Denoted at 407 and 408 are an off-axis alignment scope and asurface position measuring unit, respectively.

[0244] The exposure sequence is such as follows. Substrates 402 to beexposed are loaded into the exposure apparatus automatically or by handsof an operator and, in this state, in response to an exposure startsignal, the operation of the exposure apparatus starts. A firstsubstrate 402 is conveyed onto the chuck 1 mounted on the X-Y stage 406,by means of a conveying system, and the substrate is attracted and heldby the chuck. Subsequently, alignment marks recorded on the substrate401 are detected by the off-axis alignment scope 407, and on the basisof which, a magnification, a rotation and X and Y deviations aremeasured. Then, the position correction is performed. The X-Y stage 406moves the substrate 402 so that a first shot position on the substrate402 is placed at the exposure position of the exposure apparatus. Aftera focus correction operation made through a surface position measuringmeans 408, an exposure process of about 0.2 second is performed.Thereafter, the substrate is moved stepwise to its second shot position,and exposures are repeated sequentially. A similar sequence is repeateduntil the last shot is exposed, by which the exposure operation to onesubstrate is completed. The substrate is transferred from the chuck 1 toa collection conveyance hand, and then it is moved back into a substratecarrier.

[0245] The substrate attracting and holding system (chuck) of thisembodiment is not limited to use in an exposure apparatus. It may ofcourse be used in a liquid crystal substrate manufacturing apparatus, amagnetic head manufacturing apparatus, a semiconductor inspectionapparatus, a liquid crystal substrate inspection apparatus, a magnetichead inspection apparatus or in the manufacture of micro-machines, forexample.

[0246] Next, an embodiment of a semiconductor device manufacturingmethod which uses a projection exposure apparatus according to any oneof the preceding embodiments, will be explained.

[0247]FIG. 29 is a flow chart of procedure for manufacture ofmicrodevices such as semiconductor chips (e.g. ICs or LSIs), liquidcrystal panels, CCDs, thin film magnetic heads or micro-machines, forexample.

[0248] Step 1 is a design process for designing a circuit of asemiconductor device. Step 2 is a process for making a mask on the basisof the circuit pattern design. Step 3 is a process for preparing a waferby using a material such as silicon. Step 4 is a wafer process (called apre-process) wherein, by using the so prepared mask and wafer, circuitsare practically formed on the wafer through lithography. Step 5subsequent to this is an assembling step (called a post-process) whereinthe wafer having been processed by step 4 is formed into semiconductorchips. This step includes an assembling (dicing and bonding) process anda packaging (chip sealing) process. Step 6 is an inspection step whereinoperation check, durability check and so on for the semiconductordevices provided by step 5, are carried out. With these processes,semiconductor devices are completed and they are shipped (step 7).

[0249]FIG. 30 is a flow chart showing details of the wafer process.

[0250] Step 11 is an oxidation process for oxidizing the surface of awafer. Step 12 is a CVD process for forming an insulating film on thewafer surface. Step 13 is an electrode forming process for formingelectrodes upon the wafer by vapor deposition. Step 14 is an ionimplanting process for implanting ions to the wafer. Step 15 is a resistprocess for applying a resist (photosensitive material) to the wafer.Step 16 is an exposure process for printing, by exposure, the circuitpattern of the mask on the wafer through the exposure apparatusdescribed above. Step 17 is a developing process for developing theexposed wafer. Step 18 is an etching process for removing portions otherthan the developed resist image. Step 19 is a resist separation processfor separating the resist material remaining on the wafer after beingsubjected to the etching process. By repeating these processes, circuitpatterns are superposedly formed on the wafer.

[0251] With these processes, high density microdevices can bemanufactured.

[0252] While the invention has been described with reference to thestructures disclosed herein, it is not confined to the details set forthand this application is intended to cover such modifications or changesas may come within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. A substrate attracting and holding method,comprising the steps of: supporting a substrate by use of a protrusionprovided on a holding table for holding the substrate, wherein theprotrusion is disposed to be placed in a predetermined positionalrelation with a position of an alignment mark to be used for processingthe substrate or a position with respect to which an alignment mark isto be produced; and reducing a pressure between the holding table andthe substrate to attract and hold the substrate.
 2. A method accordingto claim 1, wherein the substrate is supported so that the position ofthe alignment mark or the position with respect to which the alignmentmark is to be produced is to be placed above the protrusion.
 3. A methodaccording to claim 1, wherein the substrate is supported so that theposition of the alignment mark or the position with respect to which thealignment mark is to be produced is to be placed at a central portion inrelation to disposition of the protrusion.
 4. A method according toclaim 1, wherein the substrate is supported so that, for differentprocessing regions of the substrate, the protrusion is to be placed atthe same position.
 5. A method according to claim 1, wherein thesubstrate is supported so that the protrusion is placed at the sameposition with reference to the position of the alignment mark or theposition with respect to which the alignment mark is to be produced. 6.A method according to claim 1, wherein the position of the alignmentmark or the position with respect to which the alignment mark is to beproduced is placed outside a processing region of the substrate.
 7. Amethod according to claim 1, wherein at least a portion of theprotrusion surrounds a zone corresponding the position of the alignmentmark or the position with respect to which the alignment mark is to beproduced.
 8. A method according to claim 1, wherein the protrusioncomprises at least one of a rim type protrusion and a pin contact typeprotrusion.
 9. A method according to claim 1, wherein the pressure of anair between the holding table and the substrate is adjusted.
 10. Amethod according to claim 9, wherein a substrate attracting force in aprocessing region of the substrate is adjusted even for the wholesubstrate.
 11. A method according to claim 1, wherein at least a portionof the protrusion surrounds a zone corresponding the position of thealignment mark or the position with respect to which the alignment markis to be produced, and wherein the pressure of an air between theholding table and the substrate in a region as surrounded by theprotrusion is adjusted.
 12. A method according to claim 1, whereinposition adjustment is performed so that a predetermined positionalrelationship is defined between the protrusion of the holding table andthe alignment mark or the position with respect to which the alignmentmark is to be produced.
 13. A substrate attracting and holding method,comprising the steps of: supporting a substrate by use of a protrusionprovided on a holding table for holding the substrate, wherein theprotrusion has an attracting groove for attracting the substrate; andreducing a pressure between the holding table and the substrate toattract and hold the substrate.
 14. A substrate attracting and holdingsystem, comprising: a holding table for holding a substrate; aprotrusion provided on said holding table, said protrusion beingdisposed to be placed in a predetermined positional relationship with aposition of an alignment mark to be used for processing the substrate ora position with respect to which an alignment mark is to be produced.15. A system according to claim 14, wherein the protrusion is disposedso that the position of the alignment mark or the position with respectto which the alignment mark is to be produced is to be placed above theprotrusion.
 16. A system according to claim 14, wherein the protrusionis disposed so that the position of the alignment mark or the positionwith respect to which the alignment mark is to be produced is to beplaced at a central portion in relation to disposition of theprotrusion.
 17. A system according to claim 14, wherein the protrusionis provided so that, for different processing regions of the substrate,the protrusion is to be placed at the same position.
 18. A systemaccording to claim 14, wherein the protrusion is provided so that theprotrusion is placed at the same position with reference to the positionof the alignment mark or the position with respect to which thealignment mark is to be produced.
 19. A system according to claim 14,wherein the position of the alignment mark or the position with respectto which the alignment mark is to be produced is placed outside aprocessing region of the substrate.
 20. A system according to claim 14,wherein at least a portion of the protrusion is disposed to surround azone corresponding the position of the alignment mark or the positionwith respect to which the alignment mark is to be produced.
 21. A systemaccording to claim 14, wherein the protrusion comprises at least one ofa rim type protrusion and a pin contact type protrusion.
 22. A systemaccording to claim 14, further comprising a mechanism for reducing apressure between said holding table and the substrate.
 23. A systemaccording to claim 22, wherein said mechanism comprises a pressureadjusting mechanism for adjusting a pressure of an air between saidholding table and the substrate.
 24. A system according to claim 23,wherein said pressure adjusting mechanism is arranged to produce asubstrate attracting force in a processing region of the substrate whichforce is even for the whole substrate.
 25. A system according to claim14, wherein at least a portion of the protrusion is disposed to surrounda zone corresponding the position of the alignment mark or the positionwith respect to which the alignment mark is to be produced, and saidsystem further comprises a pressure adjusting mechanism for adjusting apressure of an air between said holding table and the substrate in aregion as surrounded by the protrusion.
 26. A system according to claim14, further comprising a position adjusting mechanism for adjusting arelative position of the protrusion of said holding table and thealignment mark or the position with respect to which the alignment markis to be produced, so that a predetermined positional relationship isdefined between them.
 27. An exposure apparatus, comprising: a holdingtable for holding a substrate; a protrusion provided on said holdingtable, said protrusion being disposed to be placed in a predeterminedpositional relationship with a position of an alignment mark to be usedfor processing the substrate or a position with respect to which analignment mark is to be produced; and exposure means for transferring,by exposure, a pattern of an original to the substrate as attracted andheld by said holding table.
 28. An apparatus according to claim 27,further comprising a controller for calculating an error in coordinatesof an alignment mark to be produced as a result of deformation of thesubstrate as the same is attracted, on the basis of a positionalrelationship between the protrusion and the alignment mark of thesubstrate.
 29. An apparatus according to claim 28, wherein saidcontroller has one of a function and a table for calculating the erroron the basis of the positional relationship between the protrusion andthe alignment mark of the substrate.
 30. An apparatus according to claim28, wherein said controller is operable to correct the position of thealignment mark as measured, on the basis of the calculated error incoordinates of the alignment mark.
 31. An apparatus according to claim28, wherein said controller is operable to perform alignment of thesubstrate on the basis of the error in coordinates of the alignmentmark.
 32. A device manufacturing method, comprising the steps of:supporting a substrate by use of a protrusion provided on a holdingtable for holding the substrate, wherein the protrusion is disposed tobe placed in a predetermined positional relation with a position of analignment mark to be used for processing the substrate or a positionwith respect to which an alignment mark is to be produced; reducing apressure between the holding table and the substrate to attract and holdthe substrate; and printing a pattern of an original on the substrate asattracted by the holding table.
 33. A substrate attracting and holdingsystem, comprising: a holding table for holding a substrate; aprotrusion for supporting the substrate and having an attraction groovefor attracting the substrate; and a pressure adjusting mechanism foradjusting a pressure between said holding table and the substrate.
 34. Asubstrate attracting and holding system having a plurality ofprotrusions for supporting a substrate, for attracting and holding thesubstrate supported on the protrusions, characterized in that adisposition pitch L of the protrusions and an attraction force P of thesubstrate are set so as to satisfy a relation: P·L ³≦[36·E·h ²·dxdy]/[{square root}{square root over (3)}·k·c] where dxdy is adistortion tolerance, E is a longitudinal elasticity coefficient, h is athickness of the substrate, c is a correction coefficient based on theprotrusion disposition and k is a neutral plane correction coefficient.35. A substrate attracting and holding system having a plurality ofprotrusions for supporting a substrate, for attracting and holding thesubstrate supported on the protrusions, characterized in that adisposition pitch L of the protrusions and an attraction force P of thesubstrate are set so as to satisfy a relation: P·L ³≦0.00427.
 36. Asystem according to claim 34 or 35, wherein the disposition pitch L andthe substrate attraction force P are set to further satisfy relations:G·h·ρ/μ≦P≦100000 0.0005≦L≦0.005 wherein h is a thickness of thesubstrate, ρ is a density of the substrate, μ is a stationary frictioncoefficient of the substrate, and G is a maximum acceleration of a stageon which said substrate attracting and holding system is mounted.
 37. Asubstrate attracting and holding system having a plurality ofprotrusions for supporting a substrate, for attracting and holding thesubstrate supported on the protrusions, characterized in that adisposition pitch L of the protrusions and an attraction force P of thesubstrate are set so as to satisfy relations: P·L ³≦0.00427 33≦P≦100000,and 0.0005≦L≦0.005.
 38. A substrate attracting and holding system havinga plurality of protrusions for supporting a substrate, for attractingand holding the substrate supported on the protrusions, characterized inthat the protrusions include an outer peripheral protrusion forsupporting an outer peripheral portion of the substrate and a centralprotrusion for supporting a central portion of the substate, inside theperipheral portion thereof, and that, when a disposition pitch of thecentral protrusion is La and an attraction force of the substrate at thecentral protrusion is Pa while a disposition pitch between the outerperipheral protrusion and a central protrusion juxtaposed inside theouter peripheral protrusion is Lb and an attraction force of thesubstrate between the outer peripheral protrusion and a centralprotrusion juxtaposed inside the the outer peripheral protrusion is Pb,the disposition pitches La and Lb and the attraction forces Pa and Pbare set so as to satisfy relations: Pa·La ³≦[36·E·h ² ·dxdy]/[{squareroot}{square root over (3)}·k·c] Pb·Lb ³≦[8·E·h ² ·dxdy]/[k·c] wheredxdy is a distortion tolerance, E is a longitudinal elasticitycoefficient, h is a thickness of the substrate, c is a correctioncoefficient based on the protrusion disposition and k is a neutral planecorrection coefficient.
 39. A substrate attracting and holding systemhaving a plurality of protrusions for supporting a substrate, forattracting and holding the substrate supported on the protrusions,characterized in that the protrusions include an outer peripheralprotrusion for supporting an outer peripheral portion of the substrateand a central protrusion for supporting a central portion of thesubstate, inside the peripheral portion thereof, and that, when adisposition pitch of the central protrusion is La and an attractionforce of the substrate at the central protrusion is Pa while adisposition pitch between the outer peripheral protrusion and a centralprotrusion juxtaposed inside the outer peripheral protrusion is Lb andan attraction force of the substrate between the outer peripheralprotrusion and a central protrusion juxtaposed inside the the outerperipheral protrusion is Pb, the disposition pitches La and Lb and theattraction forces Pa and Pb are set so as to satisfy relations: Pa·La³≦0.00427 Pb·Lb ³≦0.00164.
 40. A substrate attracting and holding systemhaving a plurality of protrusions for supporting a substrate, forattracting and holding the substrate supported on the protrusions,characterized in that the protrusions include an outer peripheralprotrusion for supporting an outer peripheral portion of the substrateand a central protrusion for supporting a central portion of thesubstate, inside the peripheral portion thereof, and that, when adisposition pitch of the central protrusion is La and an attractionforce of the substrate at the central protrusion is Pa while adisposition pitch between the outer peripheral protrusion and a centralprotrusion juxtaposed inside the outer peripheral protrusion is Lb andan attraction force of the substrate between the outer peripheralprotrusion and a central protrusion juxtaposed inside the the outerperipheral protrusion is Pb, the disposition pitches La and Lb and theattraction forces Pa and Pb are set so as to satisfy relations: Pa·La³≦0.00427 33≦Pa≦100000 0.0005≦La≦0.005 Pb·Lb ³≦0.00164 33≦Pb≦1000000.0005≦Lb≦0.005.
 41. A substrate attracting and holding system having aplurality of protrusions for supporting a substrate, for attracting andholding the substrate supported on the protrusions, characterized inthat the protrusions include an outer peripheral protrusion forsupporting an outer peripheral portion of the substrate and a centralprotrusion for supporting a central portion of the substate, inside theperipheral portion thereof, that a disposition pitch of the centralprotrusion is made larger than a disposition pitch between the outerperipheral protrusion and a central protrusion juxtaposed inside theouter peripheral protrusion, and that an attraction force of thesubstrate at the central protrusion is is made smaller than anattraction force of the substrate between the outer peripheralprotrusion and a central protrusion juxtaposed inside the the outerperipheral protrusion.
 42. A substrate attracting and holding systemhaving a plurality of protrusions for supporting a substrate, forattracting and holding the substrate supported on the protrusions,characterized in that the protrusions include an outer peripheralprotrusion for supporting an outer peripheral portion of the substrateand a central protrusion for supporting a central portion of thesubstate, inside the peripheral portion thereof, that a dispositionpitch of the central protrusion is made not less than a dispositionpitch between the outer peripheral protrusion and a central protrusionjuxtaposed inside the outer peripheral protrusion, and that anattraction force of the substrate at the central protrusion is is madelarger than an attraction force of the substrate between the outerperipheral protrusion and a central protrusion juxtaposed inside the theouter peripheral protrusion.
 43. A system according to any one of claims34-42, wherein a free end of the protrusion is formed into a sphericalshape.
 44. An exposure apparatus, comprising: a substrate attracting andholding system as recited in any one of claims 34-43; and exposure meansfor transferring, by exposure, a pattern of an original to a substate asattract and held by said substrate attracting and holding system.
 45. Adevice manufacturing method, characterized by producing a device throughmanufacturing processes including a process for exposing a substrate byuse of an exposure apparatus as recited in claim 44.